I read a blog post explaining why interstellar travel is terribly impractical. The short answer is that stars are far away and travelling that far takes a very long time and ridiculous amounts of energy.
Anyway as a part of explaining the distances the blog gave examples of distances and one of them was the Oort Cloud where certain comets come from. Which extended to nearly halfway there. This reminded me that not only do these objects range far in-system on their weird orbits, they range far enough out that they could feasibly swap stars, and they are full of volatiles that can be used for life support or propellant.
So maybe you could rendezvous with a comet in the Inner System, use it as a place to live and propellant, rendezvous with another comet with a different trajectory, and so on, all the way to a neighbouring star system. Being able to resupply both propellant and volatiles such as water and oxygen en route should make interstellar travel much cheaper. And for most of the transit you would be passively travelling on a comet using it as protection from radiation, which should improve safety and comfort.
This would still require practical ship scale fusion power and probably "Cure for Cancer" level of medical technology to deal with long term issues of zero gravity and cosmic radiation. But both of these are AFAIK considered possible at the moment.
But given these assumptions is it plausible to use comets and the objects in the Oort Cloud as aids to travel between systems? And how much would it help? Would it make interstellar travel practical? I am not going to ask for strict science since much of what is "known" about the Oort Cloud is uncertain. And the third question is probably impossible to answer beyond opinion, but if you have a rationale why or why not, please share.
There seems to be some confusion in what I am asking and what I was already assuming in the question. Yes, I know that the cloud objects are sparse and unlikely to have perfectly convenient trajectories, so both time and delta-V needed would go up by a large factor. The question is; would the ability to supply propellants for propulsion and volatiles for life support outweigh that for a net improvement. Is there even a way to know or give a good guess?
As per Wil Selwood's answer: You can presume that they have done the groundwork of mapping the objects in the Oort Cloud and planning the hops and schedule in advance. It helps a lot with the cloud being relatively sparse and considering the investment of what would have to be a generation ship and thus very large and expensive, they'd do all the advance work they can. You can also presume that after reaching a comet they will dig in and resupply, wait in cover until scheduled burn time, then detach from the body with full supplies, and only accelerate the ship, not ship and comet.