I wanted to post some interesting 'issues' I had and how I had to fix it, just in case someone else runs across this.
It should be noted - there may be a much easier way through Terminal or modifying a file, but I did attempt to do that and couldn't find it which included changing the resolution in pi (multiple times). I'm relatively new to RPi and Linux.... however I'm pretty comfortable with coding (if not at the very least reading and understanding it).
This is an RPi3, 64gb MicroSD, I loaded Raspbian with PIXEL.
Originally I completed the install using HDMI to a 19" screen. I loaded Tunerstudio and got it working with the MS no problem.
The 7" screen arrived, and installed as needed. Everything was as expected - except when Tunerstudio loaded.
It would open/load with the bottom right 1/3 (or so) of the main page viewable, and no sliders - whether using the touch screen nor mouse I couldn't get anything else to show. Through luck, I was able to use some F keys to have the menus show up, but nothing that allowed resizing of the window.
My assumption is that when Tunerstudio is first loaded/executed through Terminal, there's something that sets what the resolution is, and it becomes hard coded (I could be wrong, but that's how it acted).
Since the MicroSD was otherwise blank, I rewrote Raspbian over (formatted and reloaded the OS), then with the 7" screen, re-downloaded/ran Tunerstudio through Terminal and all is working well.
Now if I could only get my hands on a 12V maussberry circuit (or maybe someone on here is smart enough to know how to build something similar with Digikey components....). RPi needs to be properly shut down - and it's power source is a 5V 3a USB port. There are lots of stepdown USB boards for 12V applications, but nothing that delays the power shutdown (and sends a signal) to RPi to shut down properly. Essentially what happens is the circuit has 12V constant, and when 12V switched is turned off, the board sends a signal to RPi to shut down, then I'm guessing through a timer power is cut completely to the RPi. I would have no problem buying/using the Maussberry circuit, but they seem to always be out of stock.