I'm considering converting an 18 X 18 X 18 Exo-terra into a paludarium for newts. I have a few questions I need answered before I decide if this is a project I should undertake.

Questions:
1) Is this a practical idea?
2) Would it actually be large enough? I calculated the water area would hold approx 1620 sq inches (7 US Gallons)
3) What species of newt would be most suited for this type of set up? (fire belly newts)
4) What would be a safe number of animals to house?
5) Should I construct a filtration system?