1. is the only one I don't like. I think you should use your real user agent first on any given site, as a courtesy; whether you give up or change to a more "normal" user agent if you get banned is up to you.

Oh, and for 3.: if you can, apply some heuristics to your reading of the robots.txt. If it's just "deny everything", then ignore it, but you really don't want to be responsible for crawling all of the GET /delete/:id pages of a badly-designed site… (those should definitely be POST, and authenticated, by the way).