I can’t speak to how things are on PC, obviously, but in my experience, the best way to go about Naturalist is to take it as it comes, or in specific chunks. If you’re not having luck with Farm animals, try heading down to the desert, or to the swamps, or to the mountains. Bag deer and pronghorn as you go. Try to avoid the temptation to grind, otherwise you’ll drive yourself insane.
As for Legendaries—they’re weird, honestly? You start to see them more frequently around Level 5, I think, which is also when you can start doing missions for Harriet. The missions are a rotating pool of what animals will be available in sets of 3–you’ll be able to do missions with the Night Coyote, the Golden Bear, or the Moon Beaver or something, then they’ll switch over and it’ll be 3 different animals.
But the Free Roam Legendaries are their own separate pool, with higher chances of spawning at specific times of day or in specific weather conditions, though this of course isn’t a guarantee and they can still spawn whenever. I can grab you a list of such times and conditions, if you’d like.