1. If you can find a 75, go with it. They are usually not much more money. I'd go with glass. Acrylic is expensive and scratches easier. It is lighter though.
2. I'd go with a canister. Anything 40gal+
IMO should have a canister.
3. Yes. The Wal-Mart ones are insufficient. I'd go with a Visi-Therm Stealth. They are not glass so they won't break from being hit or taken out of the water while still plugged in. Plus, they are black and easy to hide.
4. You can buy purple gravel at the
lfs. You can put it as deep as you want. I like substrate that is at least 3 inches deep. It gives me more room to aquascape.
5. At your
lfs or from an online site like
www.bigalsonline.com
6. You will need hoods (to prevent jumpers) and lights (not a must but I can't imagine a tank without them). You'll also need hiding places and misc. decor.
7. I recommend the AP Master test. It is a liquid reagent kit and I think extremely reliable. The nitrates can be hard to read when the levels are high, but when they are that high a water change is needed anyway. I recommend Prime as a dechlorinator. Cheap and highly concentrated. Lasts a long time.