In theory, yes, but such a town is not likely to be economically self-sufficient unless it has a significantly high amount of technology.
The reason is that the value of a job, and thus its pay, depends on how difficult it is to a) do the job, and/or b) acquire the skills to do said job.
Sewer workers in the real world actually make a lot of money because it is a highly skilled job requiring lots of training and certification. However, things like garbage collection, janitorial staff, farmers, retail staff, etc... are going to be low paid because it doesn't take much skill to gather up garbage, farm a plot of land, or operate a register. It may be hard work, and it is certainly a fundamental infrastructure every town needs, but the fact that literally anyone can do it means it will always have a surplus supply of available workers, and thus the value of the work goes down (basic supply vs demand curves show this). You also can't simply inflate the wages of these low-skill workers, as the fundamental nature of their job means that it will impact the cost of living in the town as a whole, lowering everyone's quality of life. All of this bodes poorly for your "everyone is wealthy" requirement.
In addition, the more wealthy a society becomes, the less likely such a society is to be self-sufficient. This can be seen very easily in the United States. As the country has become more and more wealthy due to the information age revolution, it has lost more and more of its self-sufficiency in manufacturing. Manufacturing is a lower-skill job that doesn't pay as much as say the jobs designing the products being manufactured, so people are less likely to gravitate towards them. Because they're low-pay and low-skill jobs, they also tend to be very vulnerable to undercutting by outside forces, so, in the US for example, the jobs move to where the workers are cheaper, such as China, Vietnam and India. This has lead to a very wealthy United States, but one which lacks the manufacturing infrastructure to fully support itself. Comparatively speaking with the rest of the world, in America everyone is "very wealthy," but we have become less "isolated" (and indeed it would be very difficult for America to fully isolate itself having lost its manufacturing base).
You can also see this effect in places that have even higher per-capita GDP than America such as Middle Eastern oil nations. In these nations, people are even more "very wealthy" than Americans, but they also have no ability to be self-sufficient and are even less capable of being "isolated."
All is not lost, however, as technology can, and often does, make up for the "low-skill worker" pay problem.
A couple of prime examples are elevator and telephone operators. Both of these jobs no longer exist because technology has eliminated them. In a sufficiently advanced society, it is conceivable that even difficult (technology-wise) low-skill jobs such as garbage collection, janitorial work, and retail can be done by automatons. This is actually starting to happen in America with robots replacing retail jobs and doing more and more of the "heavy lifting" in other places like manufacturing.
When it comes to skilled vs unskilled jobs, there will always be a sort of "pyramid" hierarchy. After all, it takes fewer skilled engineers to design an iPhone than it does unskilled manufacturers to build a million of them. In order to make those iPhones affordable to the people in the "middle" of the pyramid, the amount you pay the people at the bottom of the pyramid to build them must also be necessarily low.
If you want "everyone to be very wealthy" you really only have two options: eliminate the bottom of the pyramid or outsource it to someone else.
Throughout history we've done this many times. Most notably are third-world nations using it to lift their populations out of poverty. This is what China has done with American manufacturing because, although it is much cheaper to manufacture in China, the cost of living and conditions are so poor that even being paid far less than an American counterpart, the job is an improvement on life. On the flip-side, because everyone in America has gotten wealthier, the cost of living is necessarily significantly higher (or rather, the expectations on wealth are higher). This is why it isn't possible to simply lower the pay for the manufacturers to match what is being paid in China. After all, everyone still wants to buy iPhones and the trinkets that make life seem better. But, because the cost of manufacturing is lowered by outsourcing the lowest part of the pyramid, the purchasing power (and thus the wealth) of everyone else goes up, so it's a great thing for the people who don't lose their jobs. This is the double-edged sword of increasing wealth.
As far as eliminating the bottom of the pyramid altogether, this is what technological advancement does. For comparison, think of this: even the poorest American has the equivalent of 65 slaves from Roman times working for them in terms of their energy consumption for daily life.
Considering that, even in the 1800s, a single slave would cost the equivalent of a mid-size car today, that's an incredible amount of wealth for someone to have, and literally every
household in America has the equivalent of 65 slaves.
Think about something as simple as a hot shower. You wake up in the morning, awakened by your alarm clock, and take a shower. The water is provided you from a spigot, coming from you know not where, and goes down the drain to be disposed of, you know not how. This is something I think we can agree even the poorest of us in the first world have access to.
Now try doing the same thing in Roman times. Only a noble would have a slave able to wake them at a specified time. This noble would then have slaves to gather the water and prepare a hot bath. When done bathing, the slaves would then dispose of the bathwater. The bathtub itself would be a highly expensive item crafted by a highly skilled artisan, so no mere peasants would have one. Having enough wood to burn to heat the bath would be a luxury.
All of these things we take for granted today would have required immense amounts of manpower even a few hundred years ago. Even the poorest burger flipper at McDonald's has more wealth than even kings once dared to dream of. We have free (not in terms of cost, but in terms of availability) access to clean water and sewers. Food is incredibly plentiful, to the point of where we injure ourselves by eating too much (it is perhaps ironic we have reached the point where the poorest of us are likely to be obese when obesity was often a sign of being rich in past times).
Technological advancement has taken us from a hunter-gatherer society where everyone spends all of their time just surviving to the modern society where we are automating more and more of our basic survival requirements, giving us more free time to research ways to automate even more, on a positive feedback loop.
At the end of the day what all this means is that both wealth and poverty are highly relative terms. Societies are constantly redefining what it means to be "poor" and "wealthy," and any society needs a foundation of "poor" to support the "wealthy." The only way to make everyone "wealthy" is to eliminate the poor, either by moving them somewhere else where our "poor" is their "wealthy," or by using technology to make them unnecessary.
Only one of those two methods is compatible with your requirement that the town also be isolated, so the only way for your town to exist is to have technology handle all of the menial work that makes a society function, rather than outsourcing that menial work to somewhere else.
