The summary.
IDENTITY IS WHAT CONNECTS EVERYTHING
Almost every product authenticates against the same directory, so understanding identity explains more about the ecosystem's behaviour than anything else.
Plan the identity arrangement before anything else.
ONE TENANT, UNLESS THERE IS A GENUINE REASON OTHERWISE
Several complicate identity, collaboration and administration substantially — and moving resources between tenants is difficult.
Verify your custom domain before creating many users.
FEATURE DIFFERENCES BETWEEN ADJACENT PLANS ARE SUBSTANTIAL AND EASILY MISREAD
Establish exactly which features you need and which plan includes them, and check whether an add-on is cheaper for the few users who need it.
REVIEW ASSIGNED LICENCES AGAINST ACTUAL USERS
You will find licences assigned to people who left, still billed. Diarise renewals with their notice periods.
BILLING IS IN FOREIGN CURRENCY FOR MOST PLANS
So cost moves with the exchange rate, independently of your usage.
CONFIGURATION IS SPREAD ACROSS SEVERAL PORTALS
Learn which one governs which capability, and script anything repeated — portals show current state, never the reasoning.
