Neither free or Premium will go past that 80 projects. This is a limitation in place to help us provide the best service possible, so that things do not get slowed down.
This may change for Premium in the future.
Your question has been posed before. You can have up to (150) Tasks in each of the (80) Projects, for a total of (12,000) Tasks in your account. Archived Projects and Completed Tasks don't count toward this total.
The reason for the limit is database performance.
You can read more this issue by searching for the term "80 projects" in the Support Forum query, or by checking the following links:
I really need more than 80 projects. Please make this available. It would be greatly appreciated, and useful. Thank you.