I'm not sure if this is a thing yet but this way certain groups could be allowed to make more maps than others instead of everyone having a single limited number of maps they could make.

Done !
You can limit the number of map used and the number of image like this:

• imageonmap.maplimit.100 won't allow a player with more than 100 maps to make new maps
• imageonmap.imagelimit.10 same but with a limit on the number of image in the player map store
  By default without permission node I set the limit to 2147483647. If there are more than one permission node set to true for a player I take the first one found.

Nice

Limiting players so that they cant spam that many maps at once because it's happened before already unfortunately (and large maps)

As far as I know you can't make permission like plugin.size=42 you are limited to this kind of permissions plugin.size.1, plugin.size.2 ... This is not a good solution for obvious reasons (need to check a lot of perms, slow, not user friendly).

We could add something like Essentials: add a configuration option like this:

map-limits:
    cats: 2000
    dogs: 1200
    ferrets: -1

and allow to give the imageonmap.map-limits.cat to limit to 2000 maps.

This being said, I want to remind you that starting with Minecraft 1.13, the maps limit is more than two billions. That's an enormous number, more than you could imagine (all ImageOnMap installations combined use approx. 1% of this per-server-limit). So, is this really needed? Or are you asking for this feature to limit players without technical considerations?

It seems that it's possible to get a player list of perm . That make this feature trivial, a permission like ImageOnMap.mapSize.14 is now something doable