Okay, here's my synopsis:
ALWAYS shop around online and otherwise. Compare total cost (shipping included) with sourcing it locally. And always take a look at a model locally.
There's only like 3 comanies that *actually* make the LCD panels. As such, my bro's old Philips 42", My friend's 40" Dynex, and my 46" Sony look very close to the same. Ditto on my dad's 46" Samsung and his 32" LG.
When it comes to size vs. 720p/1080p, the big questions to ask are "how far away is the TV", and "how good is my eyesight." For my dad and his g/f, both with questionable eyesight, their 32" lcd for the bedroom, about 10-12' away max, 720p looked just fine to them. For me (who has eyes like a haw), i could tell the difference, but why would they shell out more for something they couldn't even tell the difference?
As for types of cables--as a general rule, HDMI is the best you can have since it carries both audio and video. One cable carries the whole digital signal. Basically, I think with your setup, if you're not running it through a receiver, is to connect the cable box's HDMI out with one of the TV's HDMI in, and the 360's HDMI out wth another of the TV's HDMI in.