IMO, Grades in courses are irrelevant in GSOC. As a mentor I don't even bother looking at that sort of thing. I just see how well they do on the qualification tasks we give out, how well the student interacts on IRC, and whether there are any things that might interfere with an effective summer (e.g. having another job at the same time, etc).
Not at all, there are many different projects with varying levels of difficulty. Everything from documentation addins to web apps, build system fixes or runtime work. We don't care what your level in school is, we care that you're excited about contributing to open source and propose a project that you can do.