go with a 4 ft t8 strip for the bottom tanks. those t5's that h.d. sells come with 3000k bulbs, so you;re looking at another $35 to replace the one's that come with it. you can get a 4ft t8 and 2 6500k phillips bulbs for $30.
and if your flooring is uneven, best bet it to go with a 4 legged stand. easier to level 4 contact points than it is to level a 4'x2' rectangle.
also, since you keep mentioning 20H tanks, future planning would dictate that you go with a stand that is 48x24, even though a 75g is 48x18. a 20H is 24" wide, if i am correct, so a 24" deep stand would allow you to place at least (3) 20's if you so choose. as far as the extra 6" on the top? you could use that space behind the tank to hide equipment or chemicals or whatever you so choose, so it;s not wasted space.
just something to make you go hmmmmmmm.......
oh....and this stand is not only cool looking, but VERY easy to build.