I would start small you could start with 2000 and experiment on sponsors and see which ones performs better with a decently CTR. You could do little test and see which one does better, I would start with small portions.
I wouldn’t use sponsors since it isn’t effective, with the recent changes that been made sponsor games are showing up less - developers have been receiving a low click through rate. OP, with the previous sponsor you did what was your CTR and impression? I would highly consider moving towards advertisements since that seems like a best approach for now.