newsalt,
This site has been really helpful for buliding my 10 gallon sump for my 29 gallon tank:
melevsreef.com
In regards to tank size, I would recommend getting a tank that is 36 inches wide. This makes getting proper lighting so much easier. 29 gallon is far more common, but the 30 inch width is an in between size in terms of lighting. Flourecent, T5 and Powercompacts all come in 24 in. or 36 in. length. So it's better to go with a 36 in. wide tank. Of'course this won't matter much if you get a MH lamp
naru