Add a client
Start them in under a minute. The rest fills in as onboarding goes.
Client readiness
Not created yet. Fill the form and add them — onboarding (contacts, ad accounts, economics, and more) fills in over the first week right after, and each gap there names the capability it blocks.
What I'd skip
Don't ask for logins or passwords in onboarding. Every access field there is a permission grant — MCC link, Business Manager partner, GBP manager — which survives them changing their password and doesn't put you in their account as them.