Hi, I was having thoughts along similar lines a few weeks ago, except I wanted to make a small, portable, all-in-one box that I can sit on top of the panel (without impinging on the outside view).
Obviously, the 7-inch display is too big for that, so I bought one of these:
https://www.aliexpress.com/store/product/UGEEK-Raspberry-Pi-3-5-inch-800-480-60fps-TFT-Screen-HD-HighSpeed-LCD-Module-3/1954241_32672157641.htmlWhich is supposed to be high resolution and sunlight readable. I've tried it with a browser running radar view and it is just about usable. I'm planning to write a bit of software to basically show the same thing as the radar display, but with slightly larger symbols and text.
I'd go along with what Ian says that it's better to run the display from a separate processor, firstly (for this stuff) I prefer to be nowhere near the processor capacity and secondly they are only £32. Also, this little display uses the same connector as the P3i radio so it would be a non-starter (I think) to piggy back it.
Having said all that, and as you suggest, using a tablet is probably the best option, especially coupled with all the advantages of Sky Demon or similar. The only reason I considered this, is that I use JeppView mobile FlightDeck sometimes which doesn't have the option to display traffic from PAW AFAIK.