For the monitor, just be sure to get a monitor or TV with a "power resume" function.
Basically, you want the monitor to "come back on" when power is restored.
Then you plug the monitor into a smart power strip that turns on EVERYTHING when the PC is turned on.
That way, all you have to worry about is a switch to turn the pc on, and you can use any ol' switch for that.
Here's the one I used in my cab
(ok, so that one +does+ take a little more effort to use as a pc switch, but any momentary pushbutton will do in reality.