Hi Oussema,
There is no limit that I am aware of on how many projects you can create. It is certainly more than 20!!
The Assignee field throughout the entire Jira family only allows one person. This is the person responsible for seeing that the work gets done. You can create a custom field that allows multiple people to be entered. We call it Assignees for some clients. It is a multi-user picker field.
Now you have no objects - start using it. hahaha
