What should I know/ask when getting estimates for a new central AC.?

You are looking at a 2 1/2 ton unit depending on how well insulated and how good your windows are also how low you like to keep the temp. It will certainly do fine on a 1000 foot house. As far as what to ask, definitely ask about the warranty should have 10 yr compressor warranty 5 on everything else is nice. Make sure it is an R410a a/c system (the newer refrigerant) The minimum efficiency you can get is 13 seer the max is about 20 so best bang for your buck is about 16 seer. In today's day and age a permit is pretty important. Check the state and chamber of commerce for complaints against the contractor. Get everything in writing!!! Ask how many techs they have, a decent company should have at least 3. Don't give them more than 20% down. As far a brands go, American Standard is good (basically same as Trane) Rheem/Ruud is at the low end with Goodman, Carrier/Bryant/Payne (all same brand) not bad, York, Lennox, Amana middle of the road. That's about all I can think of at the moment. Good luck.