Check the recommended VET list here on EBN.
As for the testicle, yes, it COULD take up to 6 months for a drop. At 4 months, the vet should (hopefully) be able to feel where the other testicle is located. There are concerns if the testicle is within the ab or external to the ab and just simply not in the sack.
One surgery can stretch the cord and place the testicle in the sack and then tack in place. If the cord is not long enough to stretch, removal is an option, only if breeding is considered.
And yes...a single testicle dog can still produce....