Not for or against your plans, so don't take the following that way... Neo-Geo w/multi cart is on the acquisition list.
As a fellow parent (of an early teenager) I've found the "lets get a multi cab" (which started my arcade insanity) was a mistake. The bonding and fun we've gotten out of tracking down, road trip pickups, cleaning/fixing, and playing individual games we really enjoy (and want to play again, and again) is greater than any multi setup we quickly tired of.
IMHO, YMMV, and other disclaimers, non-'90s fighting multi cabs suck and just never look/feel right.
I played on a Commodore 64 for years. I loved downloading and trading obscure hacked games. Some of the hacked games weren't perfect, but I never cared. I enjoyed the acquisition and variety. This has me thinking about building a computer for emulation.
I take no offense and appreciate your post, but I don't think this system will suck. We're new to this, so it's all a novelty.
I bought my first banjo for $140. I could play a song (now) on that banjo & most people (excluding my wife) would love it. I owned a Gibson that sold for $15,000. It was a better banjo. Years ago I thought a prewar was the ultimate, but now my favorite, a modern Gibson, is worth about $3k and I would pick it over any banjo. Admittedly, I added a $1,000 tone ring. How many tone rings have I bought, always looking for something better... That's another story. I buy expensive instruments w/ little thought. I barely play guitar, but own a $2,000 Gibson. I often know value on site. After years of buying and selling, it's like putting money in the bank. You probably wouldn't buy a $2,000 banjo and I wouldn't buy a $2,000 arcade game, even if each was worth $2,500.
I read a post where some guy indignantly insisted that a new guy not to get an LCD monitor over a CRT. His reasoning was so obvious that he didn't bother to explain! I had to wonder if he pick a 70" LED or a 26" console TV. I'm a dummy because I'm still not sure what he was talking about, but I'll bet he wouldn't know a tone ring from a telephone ring tone.
In the end, I whole-heartedly disagree with your post. It sounds like the multi cab was anything but a mistake if it took you down a road, with your son, that you enjoy and love.