Thanks to everyone that provided feedback while I was building this thing. I'm glad the build part of it is over and I can go on to another cab.
All hardware issues have been resolved, and I ended up using a smart power switch inside the machine to control all components and power everything on simultaneously. Next project will definitely have more planning!
I want to try out some different FEs and make a good R-TYPE skin for one and I'm going back in the tank until I come up with a good design. As always, MAME and its ROMset need continuous tweaking and I've gotten lots of feedback from friends who've played on how I can remap some buttons, enhance the gameplay, etc.
Again, thanks to EVERYONE who commented on this project and everyone who put together this great source of information and of course all the fantastic help I received. I'm glad to be a part of such an awesome community.
I definitely want to get LEDs for the 5V lit illuminated buttons, which will make 'em pop a lot more. Here's a quick pic of it powered on and the marquee lit up...
u360s play like a dream, I gotta say.