DON'T get a 55 if you want any kind of a foreground....unless you ONLY want foreground. They are too narrow to scape effectively. Trust me, I know....
For a smaller tank, 40 breeder or 50 (36x18x18") are great, for larger, 75 is the way to go.
As far as tank depth, you can always find lights that will work with any tank depth. I had a nice carpet of Hemianthus micranthemoides in my 55 with 2x96 watts PC