Hi Dave! I started Humira a few years ago, and it has done pretty well by me. I was very, very nervous about the starter doses. I have a few pieces of advice. First, the nurse may recommend you do the injections in your stomach or in your legs. For me, I have found that injections in my legs are far, far less painful, and that doing them lying down makes them no worse than a bee sting. The second piece of advice is that I usually wait until my Humira warms to room temperature, which also reduces the pain.
Don't worry about the allergy stuff. In terms of the pain, it probably will hurt, but it never hurts as much as you'd think. The starting doses are the worst, and from then on, it's a walk in the park.
I have no idea about drug reactions, but you should definitely call the nurse/doctor in advance. Humira has made my life better, so you can look forward to that!