I like the idea of the project! I understand correctly that there will be only one UST token in the system first?
Yes, you are absolutely right, this token will be used inside the system, you can sell / buy it on the main crypto-exchanges.
And for what it can be needed inside the system, that I can pay them?
Yes, anything, everything, all the possibilities that give you access, an example of use you can see on the platform Uremont, which became the basis for the platform Uservice