Re: Which route should they go with Quicksilver's costume?
I'm not entirely sure what the rationale for the twins wearing costumes will be. For Iron Man, it's his suit of armor. For Thor, he's an Asgardian. For Captain America, it's his uniform as a soldier/agent. For Hulk...well duh. And for the Hawkeye and Black Widow, they're SHIELD agents. Scarlet Witch and Quicksilver will most likely be none of that.