Will green puffer fish eat snails?  

yea they do eat...
The green spotted puffer, Tetraodon nigroviridis, is a tropical fish found in India, Indonesia, Sri Lanka, Thailand[1]. These fish can grow up to 6in (15cm). As their name implies, these fish are green with black spots. Other names include GSP and spotted green puffer.
They are omnivores. Primary foods are small snails and mollusks. Live and meaty foods are preferred by these fish, however they will eat algae and other vegetation. Constantly growing teeth require that the puffer eat crunchy food to wear them down.
This fish is a brackish water fish but survives better in a full marine environment once it reaches adulthood. It is tropical, prefering water temperatures of 24 – 28°C[2]

I don't know the answer to that but you caan do a quick search on the net to find out all the info you need.

Yes, and it's recommended to feed them snails every so often as mentioned, to keep their teeth trimmed. I wouldn't mix them with other fish, and I don't believe it's recommended mixing them with other puffers-they tend to not get along well with others. As also mentioned, they may start out as a fresh water fish, but will require a brackish set up and then a full marine/salt water set up as they get older. 10 gallon tank is kinda small for it. I have one, he's in a 20. I think they recommend at least a 20, maybe even a little bigger. Here's a good site for a puffer forum, everything and anything you ever wnated to know about them. And, if you were thinking of dividing your tank because of the puffer, don't do it. He'll need more room then that.

http://www.thepufferforum...