Most species cannot be kept in a glass aquarium. Veileds can be kept in a screen/glass combo - with alot of attention to detail. 55 gallons is pretty small anywhich way. Your cage size is really going to depend on the species you decide on.
Beginner chams include veileds, panthers and jackson's. All have different requirements. You may want to go through the species profiles on
www.adcham.com and
www.chameleonjournals.com and narrow your search.
Most chams will stress at the sight of another reptile - and snakes are a natural predator to most. Some species will be more frightened of arboreal snakes - their defense is to drop to the ground. They are so cool - you'd want to keep them closer to you anyway.
Jaylyn