How many images can I add to a single overlay?

Hey this isn't an issue yet but I was wondering if there was a limit to how many images I could add to a single overlay?
 

I'm creating a mod based off of an anime with a pretty large amount of abilities. The ability hot bar i created has 10 slots and you can interchange your currently unlocked abilities with those that you no longer wish to use in the moment. Since there was no way to set images to load based off of variables I have to add each ability icon to the ability bar 10 times (1 for each slot).

Currently I have close to 450 images on one overlay and it's running pretty fine but at this rate I'll have to add over a thousand more. I'm already pretty far into development but I figured I'd ask anyway if at any point in the near future if this would no longer work? Are there any hard limits to amount of images I can add?

Thanks in advance :D