wow, this is like tha basics of wiring...
You can install the neons now, that's no worries... taking out the dash will have no effect on the footwell area...
as for the neons, if they are your usual 12V neons, they will have a wire coming out of them, one side red, one side black... Attach the positive side (red) to your battery, or a 12V+ of some kind that you can find, and attach the other side (black) to the chassis of the car using an existing bolt... Put the switch on the ground (black) wire, then mount the switch...
Viola, neons