@Blue85 is the OG of having a tablet in a k5.
Oh man, my love/hate with on-board devices does go back awhile. Back in the 2000's I ran touch-screen PCs in the K5. This stemmed from the pain of carrying a laptop around for tuning the Megasquirt. But I set up to play mp3 files and ended up ditching the head unit after a while. For a while I had a DVD-ROM drive in place of the head unit with some kind of 12V power supply for it and a USB-IDE adapter. Never worked perfect. I had to build circuits to interface with the PC, so it would power on/off with the truck and the amps would turn on/off with the PC. Kind of sucked to have a touchscreen failure and not be able to turn the volume down.
First was the "Ramline 510", which was Pentium III. I later upgraded to the Genesys MAX, which was like 700MHz, more RAM and "transflective". In both cases it was a pain to get the touchsrcreen drivers to always work, so I carried a mouse and keyboard along just in case.
I still have the Genesys (like the 2nd picture, but with a bigger screen) with it's stainless cop car docking station in a bag in the truck. Although Android has come a long way, A PC is still way more reliable for serial port ECU flashes. For a while I had a Compact Flash GPS card in a GPS-PCMCIA adapter in the dock and an external GPS antenna on the roof. The software support was never good enough to make it a real Nav machine.
Now you can get a really nice used Android tablet on eBay for $40, so there's no need for a lot of those old school struggles. GPS, Wi-Fi, touch screen, voice recognition, etc. all BUILT-IN! I keep satellite imagery of everywhere I plan to be on an SD card and boom - navigation done.
I put a Galaxy tab in the dash of my car and found some new issues from that. I was able to use apps to make it turn on and off with the car power (actually sleep with high power saving), but sooner or later you always need access to that power button. So I opened the tab and ran wires out and mounted a pushbutton switch somewhere I can reach. Use a standard bluetooth-OBDII adapter and torque to monitor engine functions. Can bluetooth tunes to the car of course, but generally use my phone just because it's more convenient to transfer content to.
Also, temperatures a real issue in-dash. After the car sits in the sun, the battery can't charge. Oddly, I have the same issue in the winter because heat from the defroster leaks into the dash and overheats it. I've never had problems from low temp except screen fogging, but the car is garaged and doesn't really freeze overnight.