And once you install them will you loose all of your previous sims and stuff (p/b not i just want to make sure)
You can install Nightlife without University, but if you try to add University later you might have problems. It's always recommended to install them in the order they came out, but you can skip the ones you're not interested in.
No you won't lose your stuff, thats what i was worried about when i installed OFB and nightlife.And you don't really need to care about the you install them.