Significant choices and totally locking out content, is a hard thing to balance. I'm hoping, at the worst, I'll be able to share the content people wanted, and still let the player feel like they made a significant choice between two clear paths.
Stacia and Magna's paths have been misleading, without spoiling too much, I wouldn't worry about these two not "getting along."
As for the other girls, If you feel like you're "locked out" on a girl it's mostly not going to be the case. Rather, there will be content for them, but content that pertains more to the path you chose. For example, Priscilla's case: if you choose the clone, that won't be the last time you see real Priscilla, and the opposite is true. There will be content that is different for each route, but that is down the line.