Hi! For what it's worth, your handpainted texture pack is the first one I search through when making prototypes or 3D jam games. They're really pleasing to the eye, and I can usually find enough variants to make the game come together. My only complaint is I had to download each pack by hand, but that's on itch :P.
As far as old-school doom-like sprites go, if you want to provide really good ones for creatures, then they require each frame to be drawn from multiple angles. That's a lot of work, so keep that in mind. There have been a few succesful games lately that used this rendering technique (sprites in 3D environments) - Forgive me father, Project warlock, Nightmare reaper and so on. If other devs were to follow those games, then you might find customers there.