As someone who was in your exact situation about a year and half ago, I have some advised based off your post.
1. Drop Here Maps - I know, you lose all your saved places, maps, etc. Google Maps is just plain better. I fought it for years but gave in and eventually I learned that I'm happier for...
I don't see why it wouldn't work. I have a One X, but all of my 4k movies were bought on Microsoft Movies & TV so I can't verify that movies bought elsewhere show as 4k too. They should, I just don't know for sure.
Nah, I've never even noticed the fan on mine.
If you're questing of it's abnormally loud then it probably is and you should look into service or returning it under warranty.
It's definitely not an option with Movies & TV, Microsoft support has confirmed that. What I'm hoping is that one of the other Movies Anywhere members support 4k downloads.