I am sorry that you haven't gotten more replies, sometimes posts fall through the cracks or the regulars are out of touch.
As you have learned, numbness is no guarantee of no pain. In fact the more numb you are the more faulty signals seem to get through the nerves. My feet and legs are so numb that I used to stick pins into them just to see how bad it was. I still get severe burning and zapping pains as well as strong shooting pains and muscle aches.
There has been considerable discussion on this forum about SFN that doesn't show up on the skin biopsy. The biopsy requires a very significant drop off in nerve fibers to be positive, a negative result may mean that you are approaching that point but aren't there yet. Unfortunately without a positive skin biopsy you may not be taken seriously for pain management, although it sounds like your neurologist accepts it as SFN despite the result.
I have hereditary sensory motor neuropathy (Charcot Marie Tooth-CMT). Have they ruled that out in your case? I have been symptomatic since childhood,have had the numbness for about 20 years. I am 53. The numbness started in my toes and has progressed to hip level, being total from the knees down. My skin biopsy showed no nerve fibers below the knee, breaking down at hip level. My EMG is also abnormal as this causes large fiber damage as well.
You are unlikely to end up in a wheelchair from this- it is the large fiber neuropathy that causes muscle wastage. I wear leg braces now and expect to be in a wheelchair at least part of the time within a few years, but this has been a life-long process for me.
Small fiber neuropathy can be hideously painful. The safest pain relief and some of the most effective appears to be marijuana for those with safe, legal access to it. There is a big discussion on that subject here,
People are generally reluctant to discuss their pain medication as it is always best to stay with the minimum effective combination, but generally after establishing a patient on Gabapentin or Lyrica, doctors will want to add an antidepressant for its pain relieving qualities. A long acting opiate like OxyContin or MS Contin or a patch like fentanyl or BuTrans would be the last resort with a breakthrough medication such as your hydrocodone for extraordinary pain or extra activity which induces pain. Breakthrough pain is defined as pain that "breaks through" despite a 24 hour pain regime.
The bottom line for most prescribers is quality of life, does the medication enable the patient to be more active or does it turn them into a cabbage? For me it allows me to cook and do some light housework for a family of 5, go for walks, run a few errands close to home.