If I might...I would suggest that you not try to write a series based on 'audience demand'. Rather, write what you want to write. Write what interests you, don't worry about us. Personally, I love the idea of a series set in the immediate aftermath of the Enterprise series--it's a period that doesn't see a whole lot of attention here and it could be a very fruitful one for you--if that's what you want to do. If you want to write new aliens--write new aliens; if you want romance--put in romance; if you want a large cast--then fill it up! If, on the other hand, you want to keep the cast small--then do that. If you like Vulcans--write Vulcans. Don't worry about what we might like or dislike--it's your story. If you write just to please others, then there's a good chance you're not going to please yourself; but if you write the stories you find interesting and want to write, then you're going to be enthusiastic about writing them and presenting them to us and we'll catch that enthusiasm.
Follow your own course and remember, "Damn the photon torpedoes, Full Speed Ahead!"