I'm starting this now too...I got the Azure Basic and got the users to all provision but don't want to manually assign all 13,000 students. So you're saying that you bought 1 license of Azure AD Premium ($72/year), assigned it to yourself as the administrator, and then you were able to auto-assign entire groups - is that correct? $72/year isn't bad, if that's all it takes, but I'm still unclear on who gets the license assigned.