By high impact, what is the impact factor...
Yes you have to get letters from editors of all journals in which you reviewed. and they have to specifically mention that you are an expert in the field and that is why they selected you.
Yes, NSC and TSC a big diff I have seen in EB1A cases when I filed. TSC was lot easier to crack than NSC. Unfortunately, you cannot apply to TSC or NSC as you wish. It depends on where you stay/work ie the state that you belong.
You have to get letters from people who have cited your work stating how your work have helped their research. Get as many independant letters as possible for original contributions.
Authorship, you have reasonabel papers, not great
Reviewer - get letters and print email invitations etc
Regards,
Sulpha