Nice start to your project.
You said "My goal is to have it installed in the dash"
Will that monitor fit in the dash with mods eventully if you gut it and move HVAC etc? If so that will be great to have a 12.1" screen at your fingertips that looks factory.
The only comment you made that I don't agree with is:
"My one fear is that it looks tempting enough so that someone may break my windows but they will get a nasty surprise when they realize it cannot be unscrewed easily. Only caveat is that I'll have a broken window"
If they break in and even try to take it (Not just kids that run away when they hear the alarm), I guarantee you will have colateral damage before they go. You might want to throw a jacket or something over that monitor when you leave the truck until you get it flushed into the dash.
You might also consider adding a proximity sensor to the alarm. I have mine set up to chirp if someone is within about 2" of the truck (ie; looking in the windows). It will feed back to your key FOB as well. This may make them think twice.
Again, great start, I'll be following your build!