I did my first-ever *A upgrade on LX a couple weeks ago, DAR-(NBO)-ZRH, four hours before departure.

1. The upgrade confirmed instantly; immediately able to pick seats with previous LX PNR. I would assume your changed award would go through the same system just as quickly.
2. I agree that Terminal E to Terminal E will be easy to make, but very difficult to make with a shower. I'd pack an extra change of clothes in case your bag gets delayed, but it's a gamble I'd take.
3. New LX C was great! If you're giving up anything by not taking UA F, it's not much, especially if you can get a single seat. And I do enjoy grappa after dinner....