After welding or brazing, I've had great success with this POR-15 kit on gas and hydraulic tanks.
https://por15.com/products/motorcycle-fuel-tank-repair-kit?srsltid=AfmBOootNd8II6sraYHFkUthcpmdSo2SOeTAGLcOwdu4IyyN-dqaNNft
No oilfield pipe experience, but Lincoln 7018AC from HD works great with my Marquette AC welder. 100A on my machine is just right for 1/8" 6011 and 3/32" 7018AC.
You should be able to weld on max output with no breaker troubles if you're on a 50A circuit. You'll probably only need about half that for most 3/32 and 1/8" rods.
Roof first, then walls in my case. I bought a few Harbor Freight boat trailer cable winches for about $20 each that worked great to square each roof and wall section before they were sheeted with tin. Use string lines to get straight and use winches diagonal to get square/plumb.
This winter I bought a set of powerline adapters to get wifi into my metal building. I was skeptical, but it works really well. I am not a tech guy at all, so my terminology might not be exactly right.
One unit gets wired to the modem and plugged into a nearby AC receptacle in the house...
The biggest thing is the time. If time matters, don't mess around. Buy a used full size backhoe or mini-ex for the project, then sell and buy your TLB to maintain the place.
I have a 25HP Kubota and backhoe. I've done all the jobs you are planning. They take a long time on a small tractor.
I've done it with MIG many times. A washer or piece of scrap with a hole layed over the bolt will give you a place to build up more material and protect the surrounding area.
Or...adequately ventilate the space and condensation will also be minimized. I have 24" overhangs with vented soffits and full ridge vent. No condensation troubles with the building itself, but I do still get some dew on heavy machines like my tractor that warm up much more slowly than the air...