Short answer: yes.
Long answer: moving accounts / domains between plans is a pain (for us and for you) and likely to cause problems. I'd suggest doing one of the following (whichever one suits your style better)....
1) Setup everything under your account, and then create web-ids for the clients and delegate access to whatever they need access to. You could either bill them yourself, or setup different plans under your account and have them deal with the billing.
2) Setup a separate account / plan for each client, and update billing / contact information when you're ready to switch it over to them. You can then grant yourself permissions to work on their account from your main account. If you want them to deal with their own billing, this is probably somewhat simpler.