In general, you should always create a Free Space organization before upgrading to a paid plan. We want you to experience Space before you start paying for it!
Moreover, Space pricing is based on the number of active users, and this number is a base parameter during the upgrade. So, we encourage you to try Space out on the Free plan, inviting your colleagues there before moving to a paid plan.
There are some workflows in place for setting up a paid plan without registering for a Free plan first, but they are only available via our sales team or resellers.