Usually there is a main breaker in the panel (fed from the meter) to cutoff all the other circuits, the rating of this breaker determines the size of the service. But yeah, 100A sounds about right for a dedicated garage or shed service. I might look into that option myself as I would rather not have to push my house circuits right to the limit all the time.
I've seen a lot of garages and large "sheds" with dedicated 50 amp service, but 100 amp is probably more common.
It's a LOT more common for a shed or seperate garage to be on a subpanel from the main house.
I wish I had enough power and cash to invest into 600+ GPUs, I'd be making some SERIOUS money at my cost of electric.
This garage is pretty big, its probably nearly the size of the house, two massive bays with 14' ceiling and probably 4-6' between the bays. The other half of the garage is nearly as big but its more of a workshop area. Then there is an upstairs... Its like my dream! The biggest issue was that in the entire place there were 3 outlets and 3 light fixtures... thats it. I had to run new cable and outlets for my farm.
The location is right in the middle of town so electric is higher than the last place I lived. I Just have to keep an eye on profitability a bit more than some.