Great! It seems like you've done your research.
I'd modify your last observation a bit. For public defender/legal aid offices, grades don't matter as much b/c client service and advocacy skills are much more important in those environments than legal research and writing. However, in impact litigation outfits like ACLU, grades do matter.
As you may be able to tell from who I interviewed with, I have very little knowledge about environmental, so I don't know how grades work with them.
A public interest job search is difficult, but the end result can be extremely rewarding. This is regardless whether you work at an impact place where you can save the health insurance of 10,000 poor families or at a direct services organization where you just saved a single mother from homelessness. Even when your classmates have 5 offers from law firms, don't be discouraged!