Not only is it okay, it is highly encouraged! For the sake of spoilers, you might want to make the topic name a bit more vague (like not putting in their last names or something). Also… well, not sure about (Mio route) Midori, since it seems like the same case as Yusa/Misa, and we put them in the same topic, so she might be an exception
Having it made on mother’s day would be pretty cool! It’ll definitely get more people to post in the topic once the day comes along But hey, if you want to discuss it now, there’s no problem in making it now either