Yes several people in the industry offer hands on training classes… Doug Rucker, and AC Lockyer come to mind. They also offer online courses. Doug gives the hands on in Houston, AC in Florida.
In addition to this forum there are about 5 or 6 others that are completely full of all the questions you have, and will have. Training, marketing, equipment, methods, etc. Google ‘pressure washing forum’, then go there and search for roof cleaning, driveways, house washing, fences, or whatever. Search here too. Seriously, the amount of information that is freely given away in this industry is nuts. With a few weeks of research you can know the exact mixes that the top guys in the country are using, and their methods… and none of it is that complicated.
Of course, nothing beats experience… so when your boots hit the ground, it may not be quite as easy as it seemed when you were reading about it, but it doesn’t take long to get going.