i picked the 10k robux for $100 package as the baseline - the grey market has never reached that ceiling. no, when cashing out, 1 robux is 1 robux, doesn't matter what currency you paid for it. an exception was if the robux was old, from the period where you could trade tix (free) for robux, but i don't think that applies anymore
that also has a cap, you're not getting more than $6 per 1000 robux there, which is a little under double the official rate but still only 2 thirds of what users actually paid for said robux. not including the risk of the platform banning you.
which means you will get torrents whose total size is smaller or equal to 10gb, which mostly contain metadata, instead of partially seeding actual books, which come in much larger torrents
that feature has a "max terabytes" field. phones typically do not have terabytes of storage, and even if they did, people may not want to seed that much
k-id, owned by epic games, which is one of the age verification companies used by discord, already does something like what you proposed. of course, our favourite infosec twitter zoomers already dissected it. https://github.com/xyzeva/k-id-age-verifier