Gnome Warlord will work. If you find a soul orb it will be easy. If you don't then it will be much trickier.
Soul orb -> Take refreshment when you have 16 mana.
No soul orb -> Don't take refreshment until you have 20 mana. (If you even reach that much mana) since refreshment doesn't work while mana burned you'll need to regen most of your mana through potions. Try and find a pendant of mana.
Both strategies save most of your glyph conversions for the boss. A glyph on the ground is worth 90% of your mana (50% for refreshment and 40% from the potion you get).
edit: Oh yeah, for Naga try Alchemist scroll orc rogue for the same sort of crazy health/damage but no resist combo. Not sure what god to take with him though.
edit 2: So I fired up Dragon Isles to see how easy it is without soul orb and this happened. I think *literally* the perfect start to the run.
http://i.imgur.com/qhWMw.png