1. Well, the story is focused on both Yuta and 'Rika'. If the mc was an OC then the story would probably go in a different direction. I reread JJK 0 and said "This has a lot of ... potential."
2. I guess it's up to date(?). I'm trying not to forget it between builds.
3. There would be other teams but the main one will always be those two. Others would appear as allies in the story but not as playable characters or if they do become playable it will be in another team.
4. The MC won't(probably. but will change some things as the story progresses) since it is a POV. But the girls will just like with Miwa. And soon the summer will have some of the girls in bikinis.
I'll check the sync because I'm not really familiar with that.