A decent pressure washer is essential. Anything below 15 litres a minute & 3600psi is a wast of time in my opinion. Most 13HP machines will be up to that spec,.. only the cheapest and worst fall short.
A lot of ppl recommend Honda and nothing else. Honda is the best, and the easiest to get parts for or get repaired, but it can cost double what other makes do. My recommendation to someone just starting out would be to get a Loncin machine to start with, still a decent machine, and spend any spare money on accessories like a 30 meter reel & hose & an extendible lance. Market your service well, and put aside money to buy a Honda one in 12 - 18 months.
Flat surface cleaners get mixed reviews. Most ppl say that using a turbo nozzle is ultimately quicker and it undoubtedly gives better results. I would recommend a lance with interchangeable quick connect nozzles though, as sometimes the turbo lance is too powerful and can cause damage, where a 45degree nozzle still has plenty of power but isn't as harsh.
For washing brick paving you'll need kiln dried sand. When you wash, be careful to remove as little sand as possible, and the next day (Or as soon as its properly dry) you just return and brush fresh sand into the joints. The sand comes pre-packed in sealed plastic bags and MUST be dry when applied.
A supply of sodium hypochlorite 12% (try
www.mistral.ie) is handy for really dirty footpaths. This is basically a double strength un-thickened bleach which softens/removes stubborn black spots from concrete. Its especially handy on some types of paving slab where using pressure alone will damage the surface of the slab, but pre-treating with SH will sofen it enough so it can be removed with a softer nozzle, and much faster too.
For house washing a turbo injector or X-jet is a great tool which allows you to shoot chemicals quickly and easily over a large surface. I recently did a house wash (Just the walls) where green algae had covered 2 sides of the house and I didn't need to use high pressure nozzles at all. I just used the X-jet to spray the chems & wash it down after, and it came up perfect first go, saved me at least 2 hours work, and the owner was delighted as he was planning to get the house painted, but didn't need to now as it looked like new! High pressure washing would have taken longer and may have damaged the existing paintwork.