You asked 2 different questions in this post, would be best if you entered them separately.
The first answer is subjective and entirely up to you. We have both options so you can choose what makes sense for you.
The second answer is, yes everyone needs to have their own "My.PreSonus.Com" account, although only the originator of the workspace need to be a Sphere member. You can even invite non-Studio One product owners to your group. They will be asked to create a My.PreSonus.com account with no requirement to purchase software.