Retrieving Solution and projects

Hi
I'm trying to create an add in that versions the project in my solution according to a specific criteria so I have some questions :
1 - How can I refernce the solution from which this add-in has been executed.
2- How can I get each project in this solution?
3 - How can I get the selected project (if this is not applicable then get the startup project).
4- Can I add this add in to the contect menu that is shown when we press the right mouse button over a project?
 
Thanks in advance , this is urgent.