I am not a fan of early spay/neuter...especially at 8 weeks!
I would also not give the rabies vax at the same time as a surgical procedure...the dog should not be stressed when the vax is given. Both of my females were spayed at 6 months. They are both now getting older and have a bit of incontenence. Not sure if it is due to spaying early. I feed them raw and they aren't overweight.
IF I could do it over, I'd let them go thru a heat cycle and possibly do a tubal ligation instead of a full spay. I'd also do a vasectomy vs a neuter for male. I hope some vets start getting on board with the recent findings and the schools start teaching the procedures.