I'll be flying UA to MUC then LH to FRA. I've never flown a mixed-codeshare before (or to Germany).

1. When I checkin, do I need to checking with UA and LH separately?
2. Are there still issues with getting seat assignments on a 016 LH flight (v fare)? The website gives an option to choose seats but doesnt work. Haven't had enough time waiting on hold to talk to anyone yet.
3. Can I check my bag (interline) through to FRA? Not a big deal as my bag may be small enough to carry
4. Will I need to get my bag anyways when I get to MUC going through customs? Does GE get me anything over there?
5. Will I be able to use a *A lounge in MUC? Assuming a LH lounge and I assume yes since I am *G. Any recc on which one? I have over 2hrs so I think I'll have some spare time.
6. Any tips for connecting to my domestic flight? I've never been to that airport

(In case you are wondering, I didn't book directly to FRA because of I wanted to use a GPU and that's the only flight I found R, I'll be taking the train back to MUC and flying back to the US from there)