you honestly wont notice much of a difference between 1080i and 1080p. unless you plan on buying a blu-ray player anytime in the near future 1080p is actually kinda pointless. As for what kind of tv it all depends on taste. I would love to have a true 1080p panasonic plasma (that would be 1920x1080) but those are wwwaaayyy out of my price range (4 grand right now). As for settings of the tv turn down the brightness and turn up the contrast. There are MANY programs out there that will help you setup your tv. I have the sony 55" sxrd. You should be able to get the 50" for less than your budget and its a pretty good tv.
Sony 60" BRAVIA A Series SXRD Rear Projection HDTV In Black - KDS60A3000 At Abt Electronics
kinda like mine but its not.