Sorry for the delay but thanks for reaching out.
You can have up to 18 Nest Protect sensors per home and can have up to 5 homes in your account if you're signing in via a migrated Google account. If you're signing in to your Nest app via a non-migrated Nest account, you can have up to 3 homes.
I haven't heard from you in a while so I'll be locking this thread if there is no update within the day. If you have any new issues, updates or just a discussion topic, feel free to start a new thread in the community.