Well, I have TA'd Orgo 2 labs for 6 semesters (1 of honors lab) now along with a semester of Orgo 1 recitations and have also taught an experimental type of official study group for two years and summer chemistry camps, so I am not very worried about "stepping into the classroom". My teaching experiences are one of the main reasons why I want to go into academia. I also have taken all of the graduate classes at my institution required for first year graduate students in my field, so I don't think I am worried about the material much. Of course there is the transition to a new department and the different things they emphasize, but I feel it would be pretty similar to my current school in a lot of ways. I do worry about transitioning to a new city, a new school, new people, etc.
My pros of accepting the NSF I think are mainly that I would have less to transition to my first year, could focus on becoming acclimated to the new environment, focus on my classes and research, etc. If I didn't teach though, I think I would lose a lot of the chances I would have to work with many of the new and current grad students I don't regularly interact with. Another con is that I would likely teach a lot my 4th year, and I would be really focused on my research project and would want to spend that time in lab.
I didn't even know about reserve status, so I will definitely think about that option.