I dont want to set you up for failure, but take some time and look at some factory stands holding large tanks. My 300 gal factory stand is 1X4 pine and staples. No 2x4's, no 2x6's, nothing but 1x4 pine and staples. Its been holding my aquarium for 6 years without a problem. Overkill isnt a bad thing, but its not really needed either. Just make sure what you build is square and level. 2x4 strength is highly under estimated. Screw and glue everything and you should be fine. The way i see it, Anything I build out of 2x4 has got to be ten times stronger then my 1x4 pine stapled together stand.