The typical, momentary pushbuttons will work just fine -- that's what I'm using. The only time you'll need a switch with a hard on/off switch is when you're using an old-fashioned AT case instead of an ATX, and if that's the situation, you're probably using an underpowered mobo and processor.
as far as the ribbon cable goes, that's probably something you can still do. It'll be tougher to figure out what goes where, but if you can find a diagram of the pin out somewhere online, you're home free.
One bit of advice: when you do hook in the exterior power button, I'd recommend splicing the original power button back in as well, and using quick connects to connect the longer wires to the exterior power button. That way, if you have to take the PC out to work on it at some time in the future, you won't have to remove the button from your cab and take it with you as well.
Good luck,
Eric