None of those issues sounds very serious to me.

I'd just grab the two dropouts in my hands and pull them apart. Since you're talking about less than 5 mm. it doesn't take very much go permanently cold set the dropouts.

Derailleur will work fine. You'll have to radjust it a bit.

How old is your chain? I think that I'd replace it just on general principle. Trying to eke the last bit of wear out of a chain is counter productive.