1. Start with the range sensor, and then you may want to check the fluid level. If it has been more then 25k since the alst fluid swap you may think about doing that too. The downshifting feeling is normal (it's call grade logic).
2.correct.
3. doesn't sond good, is it a belt slipping?
4. could be due to the slip yolk.
I'm also one of them crazy owners with every recipt. I document it all in a notebook and staple the recipt to page. The last few cars I've sold, that has been a big selling factor of the car.