As long as the monitor is good and it's JAMMA you can do just about anything you want with it. Switching out boards or converting to a Neo Geo cab is easy. If it's a Konami/Sega or CPS/Naomi setup it'll be a little less versatile, but still have a decent selection of hot swappable games available for it.
Really the most important part of any cab is the monitor, it's a lot like PCs. The case itself is just a case, replacing the internals is relatively hassle free. I'd suggest starting with a 1-6 slot MVS board though, as carts are easy to find and swap, and the game selection is decent. Or if you're more into old school just pick up some JAMMA PCBs.
CPS1/2 and Naomi boards are more expensive and some have a problem with the internal batteries dying and then becoming pretty much useless, so for a beginner I'd stray away from those until you're more comfortable with your machine.