I'm not able to juggle so many characters and their stories at once. It's been a while since I've played STS, but I don't believe it was as story driven as HH is. More characters will be added eventually but I need to finish the current ones. That is why there is a limit on main characters.
I think there will be 12 main characters at most, I have solid plans for 2 more right now. Each main character usually gets a side character that will stick with them. And each main character has many opportunities to spawn side characters from their stories.
Who are these sticking side characters? Genuine question my friend as some are obvious and others not so much.
Lin - Obv best girl Jin
Kali - sister Lucie
Ashley - the goth girl? Kate?
Maria - recently reunited adopted sister
Android - Ellen? maybe the newly added doctor?
The Twins - each other neither are side characters and openly confess they no one but each other and the HH Mains.
Autumn - safe bet we will be seeing more of her sister as the story progress.
Still exciting to see plans for 2 full main characters are in place. Is one of these the 'third maid' you had in mind a few months back that you teased in comments?