From someone who does commercial pressure washing for a living, I can tell you this:
GPM is more important than pressure. My rig is a monster 20 HP 3500 PSI at 5.2 GPM. The only time I use my full 3500 PSI is when I'm cleaning concrete. Most applications use much less, around 1200-2000. If your using more than 500 PSI on a wood your doing damage. Look for something around 3-4 GPM range.
When you need to adjust your pressure, switch nozzles to one wiht a larger orifice. By using your pressure regulator, it cuts down on both pressue and the all critical flow. Quick connect nozzles run about $7 bux a pop on the net. For most purposes, I like to use either a 15 degree or 25 degree.
The particular brand of washer is not important since they generally use the same power plant and pump combinations. My recommendation for a pump is one made by general pump. A general pump will last as long as a cat, and is a whole lot cheaper to rebuild and replace.
To extend the life of your pump, try to rig up your unloader to where it will dump out on the ground in by-pass mode instead of looping back into the supply line. That way you can run your washer in by-pass mode continously without risk of the pump overheating since it's always getting cool water.
NEVER USE A ZERO NOZZLE, YOU WILL DESTROY SOMETHING. They ain't red for nothing.
Antifreeze works well to winterize your pressure washer. Personally I will not risk the chance at having any straight water in my rig when temps are below freezing, and running your pump dry is not good for it.
Pump up sprayers are what you should be using to apply your chemicals. They are cheap and no worries about having to run harsh chemicals thru your pump. For doing houses, get an x-jet made by the xterior company.