The guideline is that in its current state, the game takes all of about 30 minutes to play. Maybe 45 if you're a slow reader. Just play it and do what you want. If you want to try something different, play it the other way and make a separate save. We're not talking about Bright Past or The Promise with 100 hours of grinding to see if a path checks out. You really shouldn't sweat about a guide for a 30-minute game, man.
If you really can't be bothered to just try it yourself, no...thus far you can't lock yourself out of a relationship because of your choice, not without clearing knowing as much. But you can't be everywhere all at once, so you can miss some specific scenes with one girl if you're instead busy with another girl.
