So, how many shares can a user submit to participate in the weekly contest?

Shares won't be mandatory. An entry to the weekly Threads contest will consist of

• your 4 most popular posts (with or without Hive links)
• your 1 most popular comment.

I will announce the contest in several days. Now people can sign up for Threads and think about the concept of their blog/blogs. If you want, you can start posting on your Threads blog before the official beginning - just to try Threads.