I am currently MAME'ing a Jamma cab myself.
Instead of building a new CP, i just drilled the extra holes in the existing CP, and wired the buttons. The JAMMA should have the hookups for 3 buttons per player, and then the JPAC will wire up to 4 buttons per player, so even if you have two buttons wired for JAMMA, you can wire the extra 4 buttons per player on the JPAC, assuming you are doing a SF2 set up. You can see if your PC's video card will accept the Soft15KHz, or go the ArcadeVGA route instead.
Overall, I felt way out of my league when I first bought my cabinet a few weeks ago. But upon doing a lof of research and asking the people on these boards, who are extremely helpful I might add, have really helped me out a lot. I'm in the process of getting everything loaded on my PC, and are waiting for my new CP overlay and marquee before I hook everything up.