This sounds like a nice plan but requires a lot of work.
Without needing any mods you can build functional student dorms and commons in any world, so I expect that will be the same for a custom world that is added through a mod.
Students can enroll in britechester or foxbury no matter where they live. I don't know what mod you want to use for a custom uni but since we can already enroll for any available degree while living in any world, you already have a lot of possibilities in an unmodded game (If you don't mind that the uni name is either britechester or foxbury) . If I understand correctly what is said in the link you shared, that simmer built dorms and commons in another world but technically still attended one of the two universities in the game.
With the two regular universities they can enroll, attend classes, do homework, write term papers,... no matter where they live. Sims can even stay on a normal residential lot and not move to student housing.
If students live outside of the university neighbourhood they will commute to university. The difference of commuting is that your Sims will go to uni the same way the go to a rabbit hole job, this means they will vanish at the end of the lot instead of walking to a building in the neighbourhood and vanish there.
I had two students enroll and attended uni while living in an apartment in evergreen harbour. One was enrolled in britechester while the other one was in foxbury. They progressed through uni and graduated without any problems. Another sim went to uni while living in sulani. I don't know how in real life one can commute on a daily basis from a tropical island to a British uni, in this case britechester, but she managed just fine . ;) For story purposes I just pretend the uni has a local faculty somewhere on a nearby island in sulani.
