If it was me, I wouldn't set a number - I'd suggest you do them as long as you enjoy it, and then stop when you don't. It's just a fun thing you're doing; no need to unnecessarily and arbitrarily set 'rules' for yourself.
MangaDex Forums
Angry_Panda
Doedoel
Just make as much as you can without overdoing it. I mean, who knows. Maybe there's some new regulars popping here tomorrow.