A4 Allroad 2012- a few bugs?
 

Hello guys!
I am completely new to the Audi family, but had an experience with an Octavia previously. I decided to give myself a present this year and bought an A4 Allroad 2012, 2.0TDI. Car looks like it has been looked after, but now that I have it for a couple of days I noticed some things that worry me. If any of you had a previous experience please advice.
1. When driving it at low RPM it seems like the engine is over cooling (?), as temperature lingers between 70-80 degrees? It goes up to 90 if I drive it normally on a bit higher RPM's.
2. I noticed the SET button for the cruise control gets stuck, which makes it impossible to activate the cruise control normally (without getting it unstuck). I have seen there was a guide on one of the other threads, however the pictures did not load, and I am just curious if any of you have an idiot proof way to try and clean it? I have tried spraying some contact spray into the spacing around the button but I am yet to see the results (will leave it to dry a bit).

Any general advice that you would give to a brand new member of the Allroad family?

Have a great december and thank you SO much for any help.