I disagree that what sounds good on crap speakers will sound good on good speakers, this really is a case of head in the sand with all due respect. Lower quality speakers flatter your sound and mask all kinds of problems. For audio production, get the cleanest, flattest sounding monitors you can afford, and use lesser speakers (old consumer bookshelf speakers and "plastic computer speakers" work well for this) for secondary reference checks. I call it "average joe check" because it's the sort of thing most folks listen to music on--but that doesn't mean you shouldn't get your production sounding good on good speakers.
Personally, I mainly monitor with Dynaudio BM15As, ref check on Yamaha NS-10s (which are awful but nevertheless ubiquitous) and Electro-Voice Sentrys, and also take my mixes home to average joe check on poorly set up cheap plastic JBL speakers in my kitchen which is about as real-world as it gets.
Monitor size depends quite a bit on room size. Large drivers will overdrive a small room; small speakers will peter out in a big room.
Pick monitors that can be placed properly for your situation (for example, if you have to jam them up against the front wall, don't get something with rear-firing vents and so-on). I can't give you any recs without room dimensions and placement info.
I would suggest looking at modern active studio monitors--these have amps built onto them. You just take a line level cable from your gear's monitor outputs directly to each speaker. No muss with buying amps or running speaker cables, and the amps are decently well matched to the drivers which are often bi-amped as well.
You'll get the most out of any speaker by a) placing them sensibly (on massive stands and decoupling them as much as possible, never put them on a tabletop etc) and b) putting them in a room with some acoustic treatment.
Far as room acoustics, corners are always the biggest problems as they cause major bass response problems and flutter echoes. You want to absorb as much bass in the corners as possible. Look into tube-style bass trap recipes especially if space is at a premium, or flat-panel bass traps if you have the space for them (for DIY, a couple spaced sheets of Owens Corning 705 in a 4" frame covered in light fabric works especially well for this). As for commercially made products, RealTraps are great if you have the cash to spend. The smaller your room is, the more important corner trapping is as you will have increasingly severe standing waves and cancellations which your ears are positioned closer to, a lose-lose situation.
First reflection points will be your secondary problem and this can be improved by putting something absorptive on the side walls between you and the monitors. Sheets of Owens Corning 703 covered with the light fabric of your choice are ok for this.
Don't waste your money on Auralex. It looks the part but falls short on actual usefulness. Mainly it will only tame very high frequency problems, can make your room sound more choked, and won't do anything for mid and low frequencies which are really your biggest problems Been there, done that, won't be back.
