Hi Salai,
So, when we close the project, do all the new nodes get added to the solution
No, for this you need to run C&A for Implementation/Template/Upgrade projects and Check in / out for Maintenance projects with Solution.
Also, when I add a node from a solution to the project, do I need to run c&a to bring in the related document?
When you firstly add this node from Solution to Project data will be copied, for documents there is copy options.
But when you changed any data in Solution Node and want to update this to Project, C&A need to be runned from Project.
Always run C&A from object where you want to see Delta's.
Rg Dan.