External Guest User licensing demystified

HI

To looking at  Active directory B2B licensing  could I confirm the following please:

1. The fact my guest users each have an Azure P1 license on their source tenant is irrelevant.
2.  On the target tenant they can be freely invited  and not need additional licenses.
3. Again if we rely on the MFA setup on their target tenant we still don't need additional licences   
4. If we want each external user to be a member of a dynamic AD group on the target tenant, then an additional Azure AD P1 license is required for on the target tenant, for every 5 guest users.
5. Again as with point 4) if we wanted to enable MFA on our target tenant for all guest users .