Well, 20 gallons is big enough however the long might be an issue. Anoles are arboreal reptiles so height is more important then width. I have heard of people using long tanks and just orienting them vertically but I am not sure what kind of top they use. That much open area (screen) might cause a problem in terms of keeping the humidity up.
As far as reptile carpet goes, that's what I use. I find it's easier to keep clean and crikets can't disapear into it. There are two types on the market these days, one is basically a plastic grass and then other is more of a fiber. I would opt for the fibery one.
Yes you will need more lighting then just the reptisun 5.0. The reptisun provides UVB light but does not produce a large amount of heat. You will also need a white incandesent bulb to produce a basking spot and to heat. Also depending on the temperature of your room you might need a bulb/lamp for nightime use.
Ok that was longer then intended and still somewhat vauge.
These should help:
www.kingsnake.com/anolecare/
(this is where most people will send you)
www.repticzone.com/forums/Anoles/index.html
(lots of info thrown around)