Book recommendations for specific factions?

Hey all, kind of new to the universe. I started watching some of Luetin09’s lore videos, played space marine 1, working through space marine 2, and I have dawn of war 1 in my library. I kind of want to start painting minis, but I feel I have no artistic talent 😂

I really like the Tau, and Nekrons. I tend to find the xenos factions more interesting, but a lot of what I see as far as recommendations tends to be around the imperium. I don’t really have a specific faction that’s stood out for me in the imperium, although I do think the Adeptus Mechanicus is really interesting. I have infinite and the divine being shipped to me, but does anyone have any recommendations as far as books on those 3 factions? Any starting point helps.