1. You wont be able to have a serious relationship with emily if you are already in one with mia beforehand.
You can start a relationship with Mira first, then Emily. It is easier to commit to Emily then Mira, but you totally can do it the other way around. In fact you can't even get to Emily's step 8 without having advanced Mira enough that you can peak on her.
2. As mentioned in Rumah you need to resolve things with Tia asap.
You can't even get to Rumah with out Tia being your girlfriend first. You can't get to the decision on how to handle Dasan until after you make Tia your wanita. There are several descriptive warnings in game and in the walkthrough regarding the decision with Dasan. I always kill him, but ease up on telling people on how they need to play.
3. Timed events with Mira only really kick off once emily catches you together which is I think like the second time you kiss. You can take all the time you want to work on the emily relationship if you just leave Mira alone at this point.
Those appear to be timed, and were designed to feel that way, but they aren't actually.
Once the you get the notification that she is ready to undergo initiation just avoid the church during the day, she will continue to coming home at 4pm for months, until you walk into the church during the day and she goes into the basement. Not rescuing her right away puts advancing Emily on hold while she is missing, but she can stay in the basement for months. You don't have to go to the monastery until you are ready.
Emily is the only one you can get hitched to at present. I've heard there's a polyamory system coming. But right now if you do marry her the other girls will be upset. So if that's not your thing then I'd reccomend holding off on the marriage until that update.
(The first few times I married Emily, I had a committed relationship with Mira first.)
My guy let people play the game they want to. No need to police it.
Mira and Frisha are okay with it because they know before the marriage even happens.
You can fuck Kate in the butt during the day the day after the wedding, but Claire will be mad until you talk to Kate. But you only have to talk to Kate at midnight for two seconds before she is ready to fuck you, and you can get Claire involved, the next day Claire is fine.
Julia, Verena, Natasha, Tia, Katherin, Lyvia, Melissa, Anya, Yasmine, Helena, Belinda, all make a comment about it, but none of them change the available scenes.
Penny does get butt hurt about it for a week, but there is tons of other stuff to do for a week, after that everything is back to normal. You may not want that for your game, but telling others that they will lose stuff if they marry Emily is a lie. The Penny stuff isn't going to change once the update happens. It's already coded, the ability to have other marriages won't change that code.