On #3 - Do grades matter when looking for a job?
I have to slightly disagree (or rather expound) on what Stories said. I used to be an Environmental Specialist for a company and we went through some changes in which I was tasked with hiring people to replace Environmental Specialists at other branches. When people applied for the job (which required a college degree) they were asked to provide proof of their degree through a copy of a transcript. I would think this would be something that would happen with at least some of your jobs in the future and although grades may not "matter" hiring managers will likely notice your GPA and it will probably stick with them if it is very good or pretty bad (if it's in the middle they'll likely forget). I know that when I was hiring for these jobs I had a guy apply who had seemed very personable/capable when he dropped his application off. Although he was not too far out of undergrad, he had some good experience, however, I had a lot of applicants and when I went to confirm his degree I noticed that he had a low GPA from school (not terrible, but notably lower than many other applicants and I wasn't "looking" at GPA's, but I couldn't help but notice it). It was a big turn off for me because it made me think that a) he may not catch onto things quickly which would be a problem in this job where he would have no one to rely on for help as the only Environmental employee at his branch or b) He catches on quickly but doesn't apply himself which would also be a problem, without someone to watch him at the branch would he shirk his duties or do sloppy work? It would be months before I would know if he did and I just didn't feel comfortable putting him in the position. Honestly, if it weren't for the GPA he would have been one of my top picks. Shuffling through over 100 applications did not allow me the luxury of asking him to explain his lower GPA, I just passed on him and went to the next qualified person.
Anyway, I don't think it will be a deal breaker and obviously your experience/projects/etc will be worth much much more, but when you apply for these jobs you will be competing against people who have had many of the same opportunities you have had (an MPH, work study, etc) and may have similar work under their belts. At times like that hiring employers have to have SOMETHING to base a final decision on and if there is a notable difference in GPA that may be it.
Point being, I wouldn't think you would need a 4.0 to dazzle an employer, and they may not notice your GPA at all, but I would also say that it's worth doing your best so that you don't stand out on the other end of the spectrum. And you don't want to have to feel like you have to explain yourself whenever you give someone a transcript for something.
I also doubt (and am not trying to insinuate) that Stories was saying that they don't matter at all and you should just shoot for a 1.5 GPA and no one will care, I figure it was probably more along the lines of "don't worry if you have some classes that don't shine on your transcript" - but I just wanted to share my experience with it!