1: I suppose chams to avoid are the smaller sized (pygmy) chams. There more difficult to keep and to tell if they are sick or not.
2: There are 3 chams you can consider, Veileds are stated as being the most easiest (not that any cham is easy). Panthers require the same conditions (around) as veileds, vaeileds are considered better becausethey are more forgiving to heating/humidity mistakes. Jackson's are also good beginners except they require colder temps and higher humidity. But if you are able to provide constant good temps/humidity any of these 3 species are fine. Veileds are vary easily findeable and are pretty cheap, panthers are also easy to find but are more expensive, jacksons are a little harder to find and can run from 50 bux to just a little less then panthers. Sinse you said you worked with alot of reptilesI suggest panthers, They are a slightly easier cham but are very beutiful.
3: I always thought that Veileds were bigger, however with proper care a panther can live up to 9 or more years (The highest recorded age I think was 15 years).
4: I may be wrong but panthers are a little smaller, Jackson's are pretty small (around 3-5 inches SVL), Fischers are also small but they are harder to keep and are excellent escape artists.
If you go to the chameleon journals they have info on most cham species as well as very god FAQs, Go to them for a starter, select what cham you like.
also chameleoncondo.net has good care sheets on all the 3 most commen pet chams.
Good luck selecting a cham!
TheChameleonJournals
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0.2 Cats (Moora and Twitch)
0.1 Dogs (Maria)
soon to be 1.0 Panther Chameleon (Yoda)