When I built my garage I hired a local electrical contractor to do the heavy work. They upgraded the service to the house to 200 amps then ran the underground service to the garage 150 feet of trenching through rock infused clay. They put a 100 amp box in and wired one receptacle. It was all up to code and passed the county inspection.
Since then I have added 5 banks of overhead lights, 8 exterior lights, and receptacles on every wall. I rarely have to use an extension cord. I did all of the wiring myself and I can say that I was nervous every time I added a new circuit. I have a healthy fear/respect of electricity.
The nice thing about doing it all myself is that each circuit is colour coded and labeled in the circuit panel and at the light or outlet. Makes it easy to see how much load is on the circuit breaker and where any issue may develop. I'm pretty proud of myself for accomplishing this work. I was way out of my comfort zone.