I'll keep adding to this.
Suggested may be considered.
I guess I should clarify, these aren't something I'm focused on. They are just quickies and I don't really need critiques because there isn't really an end game. Some will work, some won't. They are just for fun and to get something done doodling. Each design was created with essentially one main tweak idea:
Cap: Red helmet
F4: Orange white and blue costumes, with a more monstery asymmetrical Thing.
Spidey: Work grey into the costume
Thor: No helmet.
UPDATE: newer Thor
UPDATE2: Iron Man
UPDATE3: Armored Hulk
Plan on these plus some others- Scarlet Witch, Hawkeye, Vision, Black Panther, Wolverine, Beast, Magneto, Colossus, Namor, Rogue.... etc.