So I got a Machine today, and am wanting to make a MAME machine, once I opened it up, I realised im a bit over my head.

At one point it was MK2. It was converted a couple times. Everything was still intact when I got it, minus the PCB. All other wiring is still there. The plan is to build a new CP, slide in a PC, convert the Monitor with a Jpac and boot her up. Now that im actually inside one of these machines... Things are a lot different then I expected.
The Marquee, the Coindoor, the sound (which I can remove, ill put in my own later), The monitor and some other wires i need to trace, all go into the Jamma plug and to what I assume is the Power supply. Pretty much all the wires seem to tangle together and go to multiple places.
Now I'm not sure what to do from here. I just want a pc mame setup with a real arcade monitor. Im still waiting on my Jpac, but I assume the Jamma connector plugs into that, and a VGA cable comes from that, into the PC, but what about all of this other wiring? do I run two seperate power cables? One for the PC and the one thats allready there to power the existing system? Let the Monitor, Marquee, sound etc just stay connected as is and power as is?
Sorry for my ignorance, Like I said I expected a lot different and now im thoroughly confused. I can take pictures or anything needed if it will help.