Sorry to hear of your loss. I am relatively new to Firebelly Newts, but I have done my homework. 
A 10 gallon tank (w/ a small filter) should house 5 to 6 firebellies, although something a little bigger might be a better idea.
For food. . . they seem to really appreciate the live stuff! Crickets, chopped up earthworms, ect. Some firebellies will eat the "Newt Pellets", but a live diet is the more ideal way to go.
Typically firebellies live to be between 20 to 30 year old depending on care.
I am sure some of the other members will be along to offer further advice and maybe even a link or two on the care of firebellies.
Best of Luck!
Icy