One thing I think that might be worth noting. I'm not sure what it's like in other provinces/states etc. I know that if you have a shop (ie: building), you have to have it insured. That will be for content insurance. Fire, theft and the like, NOT liability.
That being said, someone mentioned about doing rims and such.... stay away from that for the time being until you are established and are making a decent living at the detailing. why you ask?
Liability. If that customer you just did something as simple as change his winter rims and tires over to summers drives down the road and an axle snaps or wheel has an issue. YOU will be liable. You will at that point turn to your liabilty insurance to 'protect' you. Liability insurance is expensive to carry unlike content insurance.
I know at my shop (a parts store) I can't even install a set of nerf bars I sell on a 4x4 for a customer. 'If' they step on them and a bolt breaks they come crashing down and shatter their kneecap and are out of work for 6mths... I can be held liable. Same deal with a wheel.
Stick to the detailing to start with. You don't even need a pressure washer. I'd start with a one bay shop and a hose. More important than the pressure washer would be a steam carpet cleaner. You can get a used one pretty cheap if you check the buy & sells and such. Make sure it's a commercial and not a household bissel.. LOL
Use a decent product (cleaners, soaps and wash mitts or whatever you prefer & good chamois)
As for product and suppliers.. I'd take the time to make a trip to another town around your area and hit up some of the independent shops (not franchise shops) and see what they use and where they get it. You'll go broke if you have to buy all your supplies at Canadian Tire every week.. LOL
I dunno.. there's way more.. that's where my first coffee of the morning got me to so far.. .. my