Using windows on a small screen has always been the one downside to carpc’s. A 7-8 inch display just doesn't have enough real estate to function well with a touchscreen.
I'm in the process of moving from a Nexus 7 to a Latte Panda using their 7inch touch screen. Thought I might be able to cope with just the touch screen but it leaves a lot to be desired when having to use the windows on display keyboard. I've since purchased a Mokibo keyboard as a trial for a small-ish keyboard/touchpad combo to live in the glovebox for when more than opening and closing apps, maybe navigation, is needed.
I'll be using Realdash or my aftermarket ECU software. For a factory ECU car it's still super hard to look past the usability of Android with custom roms.