I actually did full fire damage build on Wyll. you have several items that can support this build.
invocation: Agonizing Blast, add charisma modify to your eldritch blast, a must pick.
Devil's sight, Wyll is a human so he doesn't have dark vision naturally. so it's would be really useful for him in dark places.
or Repelling Blast, you can push the creature up to 10 feet away from you by hitting it with eldritch blast, which you can push the enemy out of the high ground and let fall damage do its things.
spells: (4th) burning hand, scorching ray, misty step, hex, and a spell of your preference.
item: two items that related to the fire damage. the headband from rescuing the Counsellor in Waukeen's Rest. and a pair of gloves for rescuing Baelen in the underdark.