A bathroom in a HOUSE has to have a circuit that is only used to supply power to the bathroom (or bathrooms). Cant power any other outlets in the house. I dont believe that an outbuilding bathroom would have the same issues, but im not sure. I have never even looked up that code, as here in N Idaho no-one generally adds a bathroom to a standard outbuilding as they would have to heat it all winter to protect the plumbing. I see some summer use sinks/toilets is all.
As for the single dedicated outlet not requiring a GFCI...nope. That rule was tossed out in 2008. The dedicated single receptacle cannot be used unless it is gfci protected. Under current laws, ALL 120 outlets in garage/outbuildings HAVE to be GFCI protected.
A 40 amp circuit is technically able to supply 9,600 watts; however we generally only allow 80% of that as a calculated continuous load.... 9600 * 80% = 7,680 usefull load (continuous). That being said, you dont simply add all the circuits that MAY be used to determine the actual load, as the NEC allows for derates to be used. For instance no one will generally have ALL the lights, all the compressors, all the hand tools used at the same time.
Doing meaningful load calculations is very tricky, and kinda frustrating. In the last code update and load calculations seminar that i attended 2 years ago, of the 40-50 people in the class, it seamed that EVERYONE had different answers for the load calc questions.
In the OP's shop. my biggest concern is if he intends to add electric heat. Heaters are a HUGE draw on a panels load. Air conditioning not so much.
