The 18x18x24 is a great size tank for them. My 2 females do great in it. I'd just advise giving them seperate feeding areas and plenty of branches / plants to break up sight lines. If you get 2 very close in weight they should do ok. Females go for a LOT more than males, so if you really want a nice specimen, an adult male will be cheaper than a female. I' browse the trade / sell section on pangea forums quite frequently as many people will post older animals there and animals that are somewhat cheaper than going straight to a breeder's website.

I would advise some plants / cover high up in the enclosure (I use the fake magnetic vines / jungles in the top half of my tank and live plants in the ground level).

I also LOVe the acrylic feeding ledge and disposable cups pangea sells. I also have the naturalistic mushroom ledge, but the acrylic is a lot easier to clean.

Hope this helps!
Artgecko