Great ideas that will be worth exploring! I'd love to see the Fire Mages talents synergizing like this. Fire Orb is also pretty lame in its current incarnation so could definitely benefit from some reworking.
Another similar path I'm eager to explore is to have the things like vines, webs, etc. create burning clouds instead of instantly spreading. This would help differentiate from the shock spread mechanic, allow the player to create additional flame sources and just look really really cool as the fire mage sets whole swaths of the level on fire.