So far I only have Master Controller (base version) and a couple of other Nraas mods. All SP/EP, latest patch.

I particularly looking for mods that allow you to move them easier as the invite function does not always works which is frustrating when sims have relationship with non-playable/townies/tourists etc outside the neighborhood. Master controller works perfectly with sims who live in the main neighborhood, but are there any mods that alter the vanilla ways of these type of sims, such as moving, spawning etc.

I'm still rather new to TS3 so I don't know what to look for, but when playing a sim through university I found the ways to move in best friend and romantic roommates to the main-hood a bit annoying.

I'm not a fan of killing them off with the testing-cheats (as I'm not familiar with how townies/locals works in TS3 compared to TS2), so another mod I'm curious if it exist is one that prevent them from spawning? The university subhood had at least a hundreds of sims.

MasterController should have you mostly covered there.

To invite a sim over to where your active sim currently is, NRaas > MC > Sim > Basic > Invite Over.
To force a sim to move into another household, one of their own, or your own household, NRaas > MC > Add Sim (using the Household menu)
To delete a sim so it is as if they were never in your game in the first place, NRaas > MC > Sim > Advanced > Total Annihilation. Testingcheats shift-click deletions should never be used on sims of any kind, that only deletes their body but not their sim data and often leads to game corruption.

Tourists from other worlds are very different. The NRaas mod that controls these is Register.

These are not working out for you, or not what you had in mind?

Well, for example. I'm trying to move in a few premade students from University but when I try to invite her, it doesn't work, because the game says I can only invite one foreigner at the time, which is a bit confusing as I already moved in the guest with Mastercontroller. The moved in guest can apparantly invite another sim, but unfortunately the ones I want to move to the main world do not know each others.

The safest way to move a sim into a homeworld when they currently reside in another is to use MC > Add Sim > Homeworld > (filter to their homeworld). There is no limit as to how many times that can be run. Invited guests are not full-fledged sims when they show up, they are scaled down mini-sim versions of themselves and asking or forcing them to move into your homeworld while they are in that state is risky and can damage the sims if not enough sim data is available to make the transformation. Another safe way to do this is to travel to the other sims' worlds and get them to move in (join your traveling party) from there, then they should return home with yours and be part of your sim's household -- but this is more difficult to manage and sometimes we want these sims to move into our towns, but not into our own actively played households. In other words, sometimes we want them to be neighbors, not actively controlled by us as part of the same household we are at that point playing.

You can tell when you are dealing with a scaled down mini-sim and not the full version by trying to bring them into CAS (testingcheats, MC, any of them). That would be impossible to do. And yes, you cannot use the in-game invite over for a visit (from a different world) scenario while such a scenario is already running. I believe with MC > Sim > Basic > Invite Over > Homeworld > (filter to homeworld), there is no limit on the number of other world visitors, they will show up right away, not a couple of days later if they feel like it, and make their way over to where the sim inviting them is. But they are still mini-sims in that state, not full-fledged versions of themselves.

Asking or forcing already visiting mini-sims to move in is at least somewhat safer if one has a few more NRaas mods in play as they work to protect these sims from becoming damaged during the homeworld change -- those would be ErrorTrap, Overwatch, Traveler, and RelationshipPanel.