I recently fixed 5 poles in my shed. I dug down to the bottom of the poles found huge boulders under them put 3 inch channel iron on both sides bored a hole through at the top and bottom and put in 5/8 all tread and lag bolts should last longer than the shed. The worst part was my ground wayer...
I think it depends on if you live in town with a Natural Gas line or in the country with Propane.
I paid 950$ for my senville 18k unit received $450 check rebate from my coop and was able to get $300 back on my federal taxes. So I have $200 into the mini split heat pump. I usually use 1400...