For early stage HD, 2-4 cycles of ABVD (that would be 4-8 individual treatments - each cycle is 2 administrations) followed by radiation to the involved lymph nodes is a widely accepted standard-of-care.
There is some controversy lately as to whether one can skip radiation and add additional cycles of chemotherapy - this is an issue patients should discuss openly with their doctor. Both chemo and radiation have potential long-term side effects, so patients need to consider which treatment option is most appropriate for them with that in mind.
I think the PET/CT is reasonable to obtain now, and could offer valuable data. However, even if the PET shows your cancer is "gone", additional treatment is often advised to obtain full remission.
Ask your doctor to show you the NCCN treatment guidelines - they are current, evidence-based outlines of how to approach patients with various cancers. Seeing this could reassure you that your doctor is prescribing the right treatment for you.
Best of luck.