So I can see this system becoming very corrupt very fast. You did mention that it was assumed that this had flawless token protection but there are still ways around it. Assuming one of your logic situations, Person A asks person B of their opinions on a matter. Person A gives token to Person B. Sounds harmless on the surface but what if group of people A ask person B their opinion? Now Person B gets a token from all of group A. Naturally this would be done on purpose because person B is someone who has more political swing and can entice people to do what he wants more so than the people who are in group A (say a famous artist, actor, or someone with deep political connections). Now, instead of individuals getting the freedom to vote, you have 1 person using all of their tokens to vote FOR them in hopes that he actually intends to do well with their tokens and not use it for personal gain.
People would figure out how to exploit others and then use the gained tokens to then in turn use them to increase their collection until they amassed enough to do what they truly wanted. This would be perfectly legal in your system. It isn't stealing because people are giving the tokens on their free will to get a "opinion" (unless the token police are present, they wouldn't be able to see it was freely and willingly exchanged and even if they are present, the whole transaction can be faked for the appearance of legality), they aren't being duped, and not being taken from the dead. This in turn would lead a few people with many tokens that would then totally abuse the system with greed and corruption.
The premise is pretty similar to that of our electoral college in the USA with the exception that, there is TONS of checks and balances put into place. Also, there isn't a finite amount of votes. Each time a vote is needed, everyone gets to cast one to the elector. In your situation, do people get new ones? What happens after a period of time and eventually 2 people or 3 people have all 10 million tokens that were created 100 years ago? Now no one has a say but these 3 people. What are they voting for? If the vote goes to a system or something that changes law, the tokens would mostly be put into a government account. Now the 3 people who have amassed thousands and or millions of tokens can just freely cast 1 token because there is no competition and that person and their family will control everything for the rest of civilization. If the person is dying, all they need to do is ask their Heir a question and give them all their tokens in exchange and token transfer is complete.
On the flipside, maybe NO ONE votes because they only get 5. People would be too scared to vote for anything unless they know that vote will matter as to not waste it. Things that would normally get voted on may end up ignored.
I say no, this system is not long term sustainable, not how it currently is written anyways. If you want to create a balanced and fair society, there needs to be a lot more checks and balances. If you want the corruption and greed to be a part of it and you want the end result I described, then this is perfect. There are many other opinions on why this would be a bad system but that would be way too TL;DR; and I think I at least provided enough for you to think about.
Possible solution Update:
Ultimately there has to be some way to generate value and more tokens. Just like the US economy makes a certain amount of dollars off the print mills and redistributes dollars as it comes in to keep cash flowing everywhere. If we didn't print more bills and create new coins, we would have ran out of cash long ago for a majority of the population. Maybe do it based on age? At the age say of 16 when children will become educated enough on how the system works, they are granted 50 tokens. These tokens can only be used academically to further their education by asking questions. Once they turn 18, IF they go to college, they are granted an additional 50 tokens on the first day of class. Again academically based and only allowed to be used for the purpose of furthering education.
This now allows the population to become educated and learn the societal system. Teachers who collect these tokens may in turn hand out the collected tokens to the students who either are struggling and need to ask more questions or showing amazing ability to learn and granted more to speed up their process of learning. The tokens the teachers collect will be turned into the education token department to be re-distributed and re-used.
As the person ages, new responsibilities will be added and tokens in addition to the education system will be provided but still should mainly be using the education tokens while still in the school system.
Upon graduation or skipping college, the person will gain full rights to all tokens as written out at the bottom of this answer. The family tokens will be a currency used inside your own family among adults to be able to decide on family matters such as moving or buying expensive things such as a car. These can only be used in the family and are invalid for any other situation. Upon marriage, the legal binding contract of marriage enables tokens to be used cross families extending no further than aunts, uncles, grand parents, siblings (and their spouse), parents. You basically want to limit cross family to the core family name as you can run into the 6 degrees of separation and family tokens could be technically given to anyone. Every 10 years, the head of the family will redistribute the tokens and even out everyone's totals.
Social tokens work among friends. These friends are limited by only people that you have registered as one of your friends. and works similarly to the family token.
Commercial allows you to ask questions to salesmen. the salesmen in turn take the tokens and like the educational tokens, are sent back to the commercial token bureau where they will be redistributed every 2 years (high shopping turn over as people will be frequently shopping for food every week).
Political is just as it sounds. These will be used to vote on state/country wide topics. After the conclusion of the voting, the tokens will be dumped into the political token bureau and redistributed to new people of age and have their account refilled every 10 years.
The career tokens will have a system that combines the social and educational systems to allow for interactions between workers and companies.
As population grows, the government will provide more tokens into the system with careful balancing (just like money to prevent inflation and the dropping of value of the dollar). These will all be tracked electronically on a special electronic device. For the sake of argument, it is stored and done in such a way that the tokens cannot be duplicated since it is electronic, cannot be stolen because the device only pays out after bio metrics have been taken and therefore hold no value for anyone to steal. Any device that is lost or stolen (an attempt to gain money for the return of the device) will be quickly and easily replaced by a new device and the old one will become deactivated upon notification. Only 1 token per vote is allowed so that no single entity can heavily influence any vote. If you want to convince someone to join your cause, you will need to pay 1 token into the system in order to do so (basically you are voting twice but on good faith the person you convinced will vote the same as you but they do not have to, and is part of the risk you may take). The system and software/hardware that maintains the tokens for the sake of argument cannot be hacked or modified to steal/transfer/add more tokens to your account. If a person dies with a token account balance, these tokens will be distributed back to the system for re-distribution. If a person is guilty of a crime, token privileges will be turned off or reduced to match crime. Some privileges may be completely turned off such as voting tokens until X time meeting crime and or any type of rehabilitation is completed.
With a frequent redistribution, these tokens should be in supply for everyone to use, but not so frequent enough that the tokens hold no value as they are too abundant.
Education token distribution: 50 at 16 years (and teacher discretion) and 18 years if they go to college.
Family token distribution: 100 at 18 if not going to college or distributed upon graduation of college. redistributed every 10 years by the head(s) of family.
Commercial token distribution: 50 will be granted at 16 and redistributed every 3 years until the age of 22 to help learn proper budget management and be granted 200 every redistribution.
Social token distribution: 100 will be granted at 16 and the system will auto balance social tokens every year (assuming friends hang out a lot they may have a lot of what are we doing this week votes).
Career token distribution: 100 at the age of 18 or completion of college. Will be redistributed every 2 years.
Political token distribution: 20 will be at the age of 18 or completion of college and be re-distributed every 10 years to ensure that tokens are used wisely.
Maybe this isn't the direction you want to go with the tokens, but it is an idea that could keep the token system stable and with little corruption (I have not really sat and thought through all the situations but with how I have it in my head, this seems to be pretty corrupt proof for the most part). I hope this helps maybe spark new ideas!