Happy to hear you're liking it.
1. No, the outfits are just for flavour. And being able to select the locked ones is a bug, thanks for reporting it, I'll take a look at it.
2. He's not the only one, the romance routes are well marked when they are going to lock you out of other content, and you can flirt as much as you want, it will not mess up your romances.
3. No. You can play with no stress at all.