How do I add a teammate, and how many can I have?

Invite people from Settings → Team. Each person signs in with their own email and sees only what their role needs.

Seats count everyone but viewers, you included: Launch has 2, Growth 3, and Pro 5 plus 5 view-only places. A free preview has room for just you. A pending invite holds its seat until it's accepted or runs out, and removing someone frees their seat at once.

The invite link works once, for 7 days, and they sign in with that address, no password needed. If it runs out, click Send again.