For the first question, you'll always (if you're pursuing romances or not) wind up gravitating toward one crewmember above all the others. This won't lock out any intimacy with other crewmates before the lock-in, but if you're messing around romantically with compatible crew, you may be able to leverage that into a polyamorous situation. It'll depend on if the crewmembers are compatible with both each other and Rael, though, and that's much later in the story yet!
And for question the second, Event scenes do have limitations to them and some are very specifically locked to certain days. Most Event scenes, however, are viewable within a set timeframe. As the story goes on, you may start to see why they're structured the way that they are; it's a very complex web of potential. But Void Dreaming is made to be explored multiple times and in multiple ways, so just because you miss something on one run through doesn't mean you'll miss it in another!