Only your name, email and company name are required. Everything else can wait until settings — we ask now so we are not chasing you later.
The first administrator of your company's sign-on service. Setup instructions go here, so it must be an address you can already read.
Used on your invoices. Optional now, needed before your first payment.
Changeable any time in settings. Items marked Preview are not provisioned automatically yet, and will tell you so rather than pretending otherwise.