So far there are no conditions in the game where pursuing relationship with one girl would lead to closed path to another. So yeah, seems like you can pursue them all. With that said it's not pokemon style. For example Alex is concerned to start something with you until Ann basically gives her...
I don't like Netorare, but this game does pretty good job with choices to let me as a player steer the story in the direction I'm interested in. Recommended (y)
None for now. There's really not much in a game so far. But it has a lot planned so I guess I'll give it a try few months later again.
Plus the thing with LI Priscila that you can't prevent is a bit concerning for me....