1. Can you build skyscrapers? For instance, you can build one from scratch, or you can edit one – is this possible in Edit Town mode?
You can't build skyscrapers (no skyscraper shells that I can find without a mod that makes them available) but you can build buildings up to 6 floors if you count a flat roof (with, e.g., a bar, pool, etc. on it) as a floor. As far as I know, you can't build higher than that.
You can either use all the floors as part of the bar (or apartment, shop, or whatever else you put in it) or use the "level skip marker" or "hidden room marker" (round balls that look like tomb markers) that are in the buydebug section in the buy mode tab. You need to put a "public room marker" in the ground floor lobby so that NPCs can use the elevator. I quickly made a 6-floor lounge to check this out. I put a subway stop there and at a few more locations (e.g., town square, sports arena, another bar). I put a Duke Professional Juice Bar on each of the floors, including the ground floor (just to make sure that sims could use them and they'd be staffed with NPCs). I put in an elevator and a few things on each floor (e.g., TV, arcade games, shuffleboard, darts, dance floor with public speakers, etc.). Each of the bar objects was staffed with a mixologist within a Sim hour and there were a lot of Sims there doing things like dancing, playing games, etc. If I wanted the bar to be only on the roof, I would have used "skip level markers" on floors 2 - 5. I didn't use a "public room markers" on any floor but the ground floor but if you have problems without one, you may want to put one on any floor that you want NPCs to use if they aren't showing up after you put a "public room marker" in the ground-floor lobby (and elevators to all the floors).
You can do the same thing to make an apartment but as far as I know you need a mod to have NPC Sims live there. If you want to make an apartment without NPC Sims, you can do the same thing as for bars, etc., except you need to make sure to use "skip level", "hidden room", or "public room" markers. Any areas without makers will be "owned" by your Sim and within her/his control (and I'm assuming you don't want all the building to be owned by your Sim). You need to put a callbox in the ground floor lobby as well as the regular residential mailbox and some kind of trash can on the lot so your Sim can get mail and throw away stuff. (You need a mod for the communal mailbox and the trash chutes. As far as I know, you need those to have NPC Sims live there. There are also some other things you need to do if you want to have NPC Sims live in the apartment building.)
You use the same commands to build as to edit (i.e., testingcheatsenabled true, buydebug on, rbbb off (or RestrictBuildBuyInBuildings off/false)) to get access to the markers (or to get rid of them if you're editing an existing building). You may need to use moveobjects on to place things like elevators.
