Biggest problem I see is the work vehicle. Towing a heavy welding rig/service truck with a bus is going to be an issue. Without a service truck of some sort, I don't think you'll be as successful as you'd like when performing field welding/fabrication jobs.
The only other option I see is to get a large dognose or FE bus and build a 10' service bed on the back 10' of frame. Leave the rest of the bus for living space. The issue there is whether or not you and your partner can live comfortably fulltime in a bus with 10' less space on the back. Something like this: