What are your current top ten favorite games you intend to play on this?
What program are you using for MAME now?
What PC are you going to use?
A MAME arcade machine is a large investment of time and financial resources. I feel you should be able to answer these before you order parts. You don't have to answer me, but just think about it. You may have lots of both, but let the question serve as a sanity check before you start this project.
+1 I went into my bartop guns ablazin' and I really was disappointed in the final result. I'm now in the process of taking it apart and piecing it out and creating a Star Wars cab and a Nintendo cabaret. My FFJr cab on the other hand was a methodical creation that I spent up to a month on answering my own questions, doing research and making a product list before I even started cutting on my MDF.
Eric brings up a good point by telling you to ask yourself questions. Or if you will, do research. If you don't get it done at Christmas thats okay. Money doesn't have an expiration date. You can still tell the wife and kiddos that you would like arcade parts and tell them that you will have a set number when you feel you have a firm grasp on what you want.
I also found myself getting too greedy with everything I wanted on the bartop cab. I wanted emulators, 4 way games, 8 ways, shmups, and PC games. It really bit me in the ass. Now recreating the bartop (into more than 2 seperate cabs), I stepped back, and said, yes I like all of this but together it wont work. Its like dating mutiple girls at the same time. You try to get it to be cohesive but in the end they find out about each other and the ---steaming pile of meadow muffin--- hits the proverbial fan.
In the end everyone is right. Get a game list and dont be afraid to nix certain games. Say all you have are 4 way 2 button games it would be silly to buy six buttons with an Ultrastix when 2 buttons and a replica Nintendo joystick will nail it.
A good starting point would be to get your game list hammered out, go
here and put each game in the search bar you enjoy playing. It will give you a run down of the properties of the game including joystick used and how many buttons. There was a web page I used to know of where you could do the opposite (ie put in joystick used and number of buttons and it would pop out a list of games) but I can't find it.
From that point you can do research on joysticks, buttons etc and build what you need. And like Malenko said it prolly wont be cheap. You could end up just making a Bartop Arcade Joystick or going crazy like the rest of us and making a full size arcade cab. But its a hobby. Its supposed to be about having fun. Not having to worry about money. (Though having someone there to pull you back from going spend crazy helps.
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In the end, get a game list, tell the kids to save their $ for dad for Christmas and meet us back here when more questions present themselves. We'll be here to help.