With my router I cut ventilation slots in the plates for the backside of the cabinet. Before I started, I made a guide for my router using some scrap (yet straight) MDF.
Since I had never done this before, I made a bunch of test cuts until I got it right.
Using my router with the guide.
And the result of a lot of routing (and a lot of sawdust).
Service door with hinges, lock and magnets on top and bottom for perfect closing fit.
Base plate installed.
Picture of the front, really starting to shape up now!
I have had a change of heart regarding the LCD screen I was intending to use. The 23 inch 16:9 monitor I wanted to use creates a lot of extra unwanted bezel space above and below the screen. When I was toying around with Mame I was also a bit disappointed in the screen size left when I would play 4:3 arcade games. I also think the viewing angles would not be that great for people (like my child) who would differ a lot in size.
Luckily I got a great deal on Marktplaats.nl (Dutch craigslist) for a used 30 inch HP ZR30W IPS monitor. This screen is awesome! With it's own bezel it is 69 cm wide, while my cabinet interior width is 70 cm, so it is a perfect fit. It has a 16:10 aspect ratio, so that's a plus v.s. the former 16:9 as well. The actual screen dimensions are 64 x 40 cm, pretty descent. Since it is a IPS screen, instead of TN, it has far better viewing angles, while still sporting a 7-12 ms refresh rate which is not bad for a IPS screen.
Since the admin panel I planned was also a way to break the big bezel space, this is not necessary anymore, so I will drop the admin panel and place some discrete admin buttons on the cp.