I’m on a small pixelfed instance as well and the global feed can be useful for discovering users on other pixelfed instances and also for viewing mastodon posts with pictures. Similar to mastodon it will expand as you follow more people so keep an eye on it and maybe use your mastodon account to find more photographers using hashtags like #photography. Your discover page should show photos under trending hashtags as well so check for that and use search under hashtags. It does show local trending photos accounts at the moment, you’re correct. Dansup, the pixelfed developer, says in the next update for the beta app which is shipping soon and going public soon, the discover page will be expanding to show trending users and photos from across the fediverse.