I seen module for running ads and you can pay for ad free mode. I think it’s for pleroma, not mastodon.

most users are using mobile apps and these will not show ads. you may want to post ad directly to user timeliness but any app can block posts.

I seen larger Japanese instances display ad, I have no numbers if this is more effective than donations.

you can follow any user by pasting his name or link into your local search box

searching content is limited to portion of /r/fediverse your server knows. Server knows local content and all content that somebody from your local server follows.

Larger servers know larger portion of /r/fediverse - you can go to them, search there and paste results to your smaller server and follow.