Welding can indeed be done by the amateur builder.
Many to most people who have built an aircraft have very likely not undertaken anything like it before, and they generally turn out the best work.
I built a wooden aircraft, I did need help with some metalwork machining and welding - those were beyond my capability and equipment.
Wood, fiberglass, fabric and paint, instruments and wiring, I did the lot.
I was gong to jump in earlier.
You can amateur-build Serial No. 2 off the plans you have, and you can change anything you need to along the way.