I don't track user behavior on here. I'm not sure what I'd do with those data. The communities are also very quiet here. Most of the activity is from the auto poster bot.
Regarding donations & costs, I can certainly put something together. I should keep Opencollective updated with expenses; you can see it all there. I typically merge the expense of all the discuss.online services. Are you more interested in just the cost of the Lemmy instance? We also have the matrix server, pixelfed services, and Mastodon services.
I could discuss how I'm attempting to lower costs here soon. I've been looking to cut the cost by sacrificing some disaster recovery and stability. I wanted to be the most stable instance; however, the roll of the dice hasn't brought in major communities over, so it all seems to go to waste. We only have about 35 active users by the current census. We'll see how that grows or changes, but that will drive some decisions regarding scaling down.
There are some ongoing plans that I'm not ready to announce openly yet; it will be a significant change that will improve lots of things in the coming months. I've been working on some backend improvements and a new front-end. I can talk more about what's coming in the coming weeks when things are more ironed out. It's huge.