Some answers:
1.) Your Sims can become a witch/warlock by befriending one of the grand high witches/warlocks on a community lot. Barring any default replacements, they're damn easy to spot. When your relationship is high enough, you can ask them to teach you their craft. You also gain access to two secret lots afterwards, and can buy spell ingredients (and replacement spellbooks/cauldrons I believe) from them as well. If asked, they'll also supply you with some useless advice about practicing magic.
And since someone is bound to ask: witch = female, warlock = male. 2.) Yes, you can make your own apartments. It's done much the same way you build a Dorm, with two exceptions:
- You need to place an apartment door (the ones with the floor mat - I can't remember their name) for each unit you'd like to mark as a rental unit. This is similar to using the 'Mein Door' to designate Dorm rooms.
- After your apartment is built and is to your liking, you need to use this building cheat: changeLotZoning apartmentbase -- this will designate the lot as an Apartment. Save, exit, and test. If you wish to switch the lot back to a residential lot, just use changeLotZoning residential and you're done.
3.) No, you can't. To switch between families, you need to exit the lot and re-enter it choosing the family you wish to play. You can still interact with the other families on the lot with the family you're playing.
4.) A building party is a useless party event the landlord holds on the weekends. It's not really all that exciting.
5.) I have no idea. The pirates never bothered to include the manual in my copy of the EP.