Good work so far Shookie. That's looking like a pretty deep CP. If your aim is to play most if not all games I agree you need an analog flight stick in there and will have plenty of room. What about gun games? I would also look at your current position of the spinner. Chances are you will want a place to rest your arm / wrist over time and it looks like you have buttons and a joystick in the way depending on your play style. I revisited my layout more recently after taking a poll on that and made a few adjustments. Think about a 4.5" resting area around each of your sticks and buttons as a general rule of thumb.
As far as art goes, you got your fair share of warnings and classic responses. I'll try to offer some thoughts since I too am looking to incorporate lots of game art into mine (although merged into a theme).
First, the big disclaimer. Art can be highly subjective! If you're aiming to please the masses, you will find common approaches that work better than others. Given you've already stated it's just for you, then you do you. Asking for feedback suggests you would like to take other thoughts into consideration. It doesn't mean you have to follow it though.
As far as general aesthetic feedback, I think a consideration is balance of how busy an area is, which is often driven by contrast, and the overall user experience. The side art is designed to lure people in and quickly identify the game. The CP should have art that compliments the control layout so it's easy for a player to understand the primary controls. Even though traditional arcades didn't really have the mass collage / multi game representation, take a look at several designs and try to understand why one design catches your eye over another. Then try to follow those principals and incorporate your spin on it. For the CP, even though it's only for you, I would still play around with balance so even if you have all those characters, it blends a little better and your controls pop a bit more than the artwork. This can be done with contrast adjustments, color washes, segmenting themes per player, etc. There are examples of multi game art out there at the print shop sites and some are more successful than others at making it all work and not just come across like bumpers stickers on a car that's collected 20 from each state. You ARE making a 4 player, so that suggests others will be playing. You might not care about their aesthetic preferences, but at a minimum you should make sure the art makes their play experience easy to understand and enjoyable.
I know it's a pedestal but you might be able to incorporate a Marquee on the front of the CP. Not sure I've ever seen anyone do that yet.
If you do, be sure to call it "Arcade" in big bold letters. Mike A loves that too.
I first attempted to do most if not all of my suggestions in the renders I have at the beginning of my build thread. It works ok, again being subjective, but I'm not happy with it yet either. I got a lot of the same feedback you did. I quickly realized I should probably focus more on the build itself first and then I can wrestle with the art afterwards, and even if it takes another year to be happy, that doesn't prevent the build from being completed enough to enjoy. I can't remember how many characters I have in the current art, but it's probably around 100 or more. I think a lot of what helps it feel a bit more cohesive is balancing out the art styles and the colors to control the contrast and general theme palette. All the characters wrapped around the edges of my CP are a purplish hue on the black background with balanced contrast so one isn't sticking out like a soar thumb next to the others. All are pixel art from screen shots which also helps keep their styles more consistent. The side art is where it gets trickier because unless you want giant pixel art, you typically have different vector based art styles of characters, logos, etc. Working those together in a cohesive way is a lot harder.
As a bit of encouragement, several months back someone posted an 80's themed cab that had pink and green neon t-molding and incorporated the classic retro sunset, Ghostbusters, the Delorian, and a bunch of other games quite successfully (IMO). It felt cohesive, right at home in the 80's and very retro. I'll edit this post if I can manage to find it again. It can be done, but it's a lot harder to do that than picking a single theme for a game that someone else already mostly defined for you. Or just pick a generic style that isn't necessarily tied to a specific game at all.
Have you thought about what you're going to call it? That name can help your art theme too. Anyway, if I were you I'd focus on the build first and your CP layout. Get that all exactly where you want it and play test if possible, and then solve the art side of things.
Good luck!