Yeah, you have to make decisions and cut some stuff, because either you end up with a CP that is so stacked with controls that you don't dare _use_ any of them, or they're so wide-spread that your cabinet looks like a plane with a control-panel wing. Make choices, make decisions, spend a little bit more for some of Oscar's adaptor plates, etc. (i.e. do you _need_ a dedicated 4-way pac-style stick? Or would Oscar's restrictor plates really give you what you need?) Are you adding a control that is only applicable to 5 games? Do you _play_ any of those games, or can you live with limited functionality? (i.e. Discs of Tron and the push/pull spinner. While the PP Spinner also works as a normal spinner, it is an extra expense.)
Another thing to consider is that some combinations of controls don't really work out, even with all the updates and patches. A friend of mine was never able to get 2 spinners to work to his satisfaction, even though they would have been nice for Super Sprint and the like.
I would recommend looking through the cabinets and control panels that have been built and listed here. There are just as many negative examples as positive examples. Learn from all of them. I know, I know, this is all a labor of love, and if someone likes their control panel even though it has 7 sticks, 40 buttons (with no particular style or scheme), 2 trackballs, a thrustmaster analog joystick, 3 random steering wheels, enough random lighting to make a ricer jealous and is approximately the same size as a Mini Cooper, it's still theirs and they presumably love it. It would drive me batty.