The top control panel is 37''inches by 13.5''inches, and the width is the same as the sides of the control panel. The corners also are rounded off.
As far as the coin panel, yes you can re-use it. You'll need an ipac to interface it with the computer (along with the rest of your buttons & joysticks). The ipac2 has a spot for 2 coin mech wiring. It's extremely easy to interface as long as the coin mech is intact including the coin switch at the bottom. Just make sure it's grounded properly by daisy-chainning the common grounds together and then to the ipac. If you want the lights to go on for the coin inserts, you'll need a 12v source to supply power to them. I just hacked up some molex wires from the pc and used the yellow and black wires to provide 12v to it from the pc power supply.
The red and black wires heading towards the coin counter are the ones that provide a very brief instant of power that triggers the counter, mine i think was rated at 24volts. If you want to try hooking it up, just do a search here on "coin counters" as this topic has been covered more indepth there. I believe it has schematics for hooking one up in a mame cab. If you don't want to bother with all that, just toss it. It's not required for operation.
That switch on top of the cab (kinda obvious) is the main power switch. Supposed to turn on the marquee light, transformer on the bottom of the cab ->monitor, & suppling power to the 15amp psu which in turn powers the jamma board. For mame'ing, i just have that switch power on the computer by using a smart strip power strip (say that 10 times fast), which then turns on the marquee light & transformer/monitor.