You will definitely want a crew cab. I kick myself everyday for not wanting one when I bought the truck about 12 years ago. The back seat is really only good for small children and throwing some junk back there, plus trying to load it is a pain because the suicide door does not swing all the way back to the bed like newer trucks.
As far as years, if you are planning to get into the 500 to to 500+ rwhp range, then a year 2000 would be the best due to forged rods and quirks from the E99/L99 worked out.