find some live rock from a local club that you can buy for a 1-$2/lb. Get some sand from them too and add their live sand to some unseeded sand. this will give you a good base. depending on the density of the rock, the amount and size of fish and your aestetic prefernce, I would go with 50-100lbs or so. I cheated and bought lava rock as the base and then fronted it with the live rock. But beware if you use lava as you have the leach any impurities out in a vat of water for a few weeks.
as for the sump/ refugium, i highly suggest doing it. But have the tank drilled for the overflow on the back. trust me do it right the first time. You should be able to have a lfs drill it for cheap. No overflows ever when the tank has a built in overflow.
When it come to stocking, I beleive the newest FAMA magazine has a great article on this.
buy lights again from a local club or ebay. get t5's or compacts for this depth. if you want sps then you need metal halides.
hold off on the skimmer now, wait a month or two to save money and again do it right. ASM makes cheap but effective in sump pumps. Again, ebay or local list for purchse.
I have a 560 gallon tank, and I am currnetly building a 750 with a 300 gall refugium, stand, with all lights skimmer, rock, sand, pumps. etc. etc.etc for less than $2500
good luck