14' walls for a loft sounds like a damn good plan
It will be stand alone it will be closer to house and no real need for it
Didn't plan on putting plumbing in, It's the one thing we didn't do and should have. The $$ to drop a line from your house or well is cheaper before you start, then after you finish. Trust me
having a wash station AND shitter real close, versus running to the house during a Wyo snow storm. You will be glad you had one.
I'll have to look up tax info, the slab after is interesting information.
If it sits on the slab, it's considered a permanent structure. Most if not all non commercial metal buildings have a slab poured after the structure is up.
I was thinking a wood burning stove for heat... freebie (ish)
Now you have to factor in adequate ventilation, insulation (to code) for the stove. Supply of wood for X years. Fire proof (to code for ins) storage for any combustibles, since the stove is considered an open flame.
You don't plan on insulation? Kiss any form of heating goodbye
Are there more benefits of wood vs steel of vice versa? Forget wood.
Wood frame is considered another permanent dwelling as it's going to be on (see above) slab / foundation. There's (IMO) more hassle code ,tax and building wise to wood frame than what's called a pole barn / steel building. YMMV