Welcome to the forum and congrats on your TT.
If you're very new, there is a lot to learn but, it's fun stuff.
Don't get too concerned about the tank sensors not working properly. They're not known for always being accurate.
I assume you are plugged into shore power?
The battery should be charged and all connections clean and tight before you start to diagnose any electrical problems.
Read
The 12 Volt Side of Life, it may help you understand the 12 volt system a little better.
Many of the parts you need can be found on Amazon. Decide what you need and start looking.
Don't hesitate to ask questions on the forum, there is a lot of experience and information available.
I think the first important thing is, check your roof for leaks, rips or possible problems. A small leak can cause a lot of damage if not repaired quickly.
Eternabond and
Dicor Self Leveling Lap Sealant are two of the best products for rubber roof maintenance and repair.