I can weld but I'm no welder.
Welders have come a long way over the last couple of decades. Once a DC welder cost many thousands, now you can get a DC inverter welder for a couple hundred, not the same as a big one of course but you aren't going to be burning rods all day long.
For most little jobs encountered on one of these bikes is little more than a tack here and there unless you are into modifying frames which takes some serious skill to do safely.
As Sidewinder says start small, work your way up.