I have a 55 right now, but plan to upgrade to a 75 very soon. The 55 is the same length as a 75, it's just 12" instead of 18" wide. I plan to keep the same lighting, fixtures, etc since the only difference is 6" in width.
Most tiles come in 6" and 12" squares, and I have four 12" squares in there right now. When I upgrade, I plan to take the same tile, cut each square in two, and insert four 6"x12" tiles down the middle. I'll get two more 12" squares and cut them in half to get the 6"x12" tiles.
I have a 160w SB MegaRay in a DeepDome hanging from a ZooMed lamp stand over one end of the tank. I've got two 18" flourescent lights across the rest of the tank, just for additional lighting. I also have a 150w CHE in a dome that comes on as soon as the MegaRay goes off, to keep the viv temps up at night. We don't have heat in Pudge's room, so we have to really watch her nighttime temps this time of year.