Microsoft 365 Admin Configuration

I need an experienced Microsoft 365 specialist to get my admin centre properly configured, with a clear focus on user and group management. The tenant is brand-new, so everything from the first user creation to licence assignment and role-based access still needs to be built. We cannot access our admin account because the main account is attached to an email that doesn't exist

Here is what I expect to walk away with:

-Access as an admin to our microsft account with the ability to send calendar invites to people outside of the organization from the account.

Just the core admin groundwork inside Microsoft 365 to get it all set for teams calls. Remote configuration is fine as long as confidentiality agreements are respected.