Awww Demelza has a lot of RL people wanting to be her BFF, haha. I think clearly this means your next character has to be a 5th year to be friends with Demelza and Marietta.
Yakov has managed to avoid being fat so far. He must have an awesome fast metabolism. I think it will all catch up with him in his mid to late 20s which could be a bit of shock to him. But yeah, he talks about food constantly, so they can always talk about that.