when humans summon spirits do they look like humans?
no, not really (except for perhaps a spirit of man).
If their tradition is exclusive to the human metatype, and all about being human, as the Path of the Wheel is restricted to the elf metatype and all about
being elfy, then sure- I think that would be appropriate.
if you want some flavor to the spirit of fire that the mage summoned perhaps use some faerie or nature inspired descriptors?
This sounds like an appropriate idea. I do, however, prefer not to link Path of the Wheel to a more recent Earth mythology. Since the philosophy goes at least all the way back to the 4th age "Earthdawn" era, I like the idea of it being more tied to that. How much more mysterious would it be for someone who thinks they know all about magic to see a POTW caster/summon use some magic and not recognize its trappings?
Having said all that, Earthdawn (the game) itself is heavily based on medieval Earth mythology, so maybe that's not so far off after all.
after all both of the tir nations are dominated and pretty much run by elves. kind of.
As I understand it, they're quite explicitly run by elves, with a few notable exceptions.