So is there a damage cap, or are all of the numbers below 9999 to make the picture more readable?

I think it will crash after 31 digits. Perhaps? RPG20XX has you define your own stats, derived, etc. anyways so it's all up to you. I did mention it takes color from the current system graphic, so that means you get 14 colors and patterns for use in "damage" numbers when you usually only need 4.

You could have three times as many stats as Dark Souls if you really wanted to. It might not be good game design, but RPG20XX can't and won't stop you.

Considering that derived stats are just event scripts, and that it doesn't sanity check that you aren't using nonsensical commands, lots of things are possible. I'm only imposing limits on things that could cause unintentional crashes and bugs. If you go past 88 miles per hour, I'll just assume you know what you're doing.