Size
You're limited to 75 if you want to stay under 20"high. 90, 110, and 120 are taller than 20".
Lighting
Most suspended pendant lights or lights with clip on legs are either compact fluorescent or metal halide. These lights are normally used with plants and are more expensive than regular florescent step lights.
Filtration
Have you considered a sump? It goes under your stand, so no visibility issues, and you can make one yourself with a spare 10/15/20 gallon tank OR a tupperware storage tub. This also allows you to place heaters in the sump, not the tank, so no visibility problems there.
Have you talked to anyone at your lfs about a package deal? You should be able to put together a 75g tank/stand/canopy/et for $1000 or less.
You may want to search the forums on 2nd floor aquarium placement. I've seen a post about floors sagging ( in the last 2weeks). Water weights 8.3 pounds/gallon. That’s 700 pounds or so just in water and tank. Something to think about.
Good luck. Post pics when its up