How exciting, CupofJoe. What an adventure, and it sounds like you have great OBs.
My first pregnancy I opted out of everything possible (I'm RH- though). Then when I had to transfer my home birth mid-labor to the hospital and was "GBS unknown" I got two nice big bags of antibiotics. Thanks. Also, I wonder how much of my anxiety about my baby at birth led to the transfer, but all that is conjecture. My second pregnancy, I asked, "What will they say at the hospital if I haven't done this?" and did it. I saw my healthy baby at 20 weeks, and I had a wonderful home birth.
This time, I'm feeling calm and collected again. But we've had two friends recently have babies with problems (Down's Syndrome and a congenital heart defect), and I think that I will probably opt for the scan again as I know hospital birth may change everything. I may just do the GBS swab and be pretty minimal with other things again. I have not done the gestational diabetes test, though. I just used a glucometer for a few days.