Hi nateco & welcome to this forum.

Q - Is this something one lives with forever?
A - Depends if the cause can be found and recified, nerves can regenerate.

Q-Can it reach the stage where a limb must be amputated?
A- No.

Q- 3. sorry I live in Australia so another member may be able to help you with this question.

Q-4 or should I start with vitamins?
A- Yes, I would include supplements plus pain relief drugs, if your nerve damage is from prediabetes as mine was then I would definatly get these supplements, R lipioc acid and gamma-linolenic acid 480 mg daily, plus a multi B taken with breakfast plus B12 [ methylcobalamin] 1-5 mg daily taken on an empty stomach .
I also had to change my diet and loose weight to get back to normal blood sugars levels, loosing weight is a slow process and so is nerve regeneration.
good luck
Brian