I appreciate the care you're showing here.
If you upload something with a width or height greater than 2000 pixels it will get resized to be within that limit. That stops the most egregious wastage.
It depends on the content, a bit:
Quality stuff like https://piefed.social/c/artporn will be kept online 'forever' but I've set things up so that quite a lot of communities automatically delete posts after 6 - 12 months. Spam as many memes as you want I don't care they're going away after a while anyway.