You should start a new thread with this topic as it may get lost here.
Your budget is VERY tight. Mark at
www.pressurewasherzone.com would be the guy to talk to. You are going to need at least 200 ft of hose (non-marking) if you are going to keep your machine on your truck.
If I were you I would spend less on the vehicle and budget more to equipment. A '98 E350 extended van might run you $2500. Four gpm/cold water machine $1500. Hose reels, supply hose, pressure hose, wands, guns,a decent downstreamer, and an X-Jet will set you back about $750. Insurance is going to be another $1200. Graphic design for your logo and business cards, printed marketing material and a decent starter campaign are going to be $1200. QuickbooksPro will be another $200. Starter chemicals, figure about $250. Oddball accessories like chemical application pumpups, extension wands, brushes etc factor about $200. Optional: Surface cleaner for concrete add $600.
This is a mediocre setup that will get the job done for housewashing and residential concrete. Your total is already $8400 if you include the surface cleaner. If you are going to do decks you will need tools specialized for that (sanders etc)
I also didn't factor in any licensing costs or legal fees to set up your business entity. It sounds like you want to do things right. Do it right now, write a business plan and you may actually be still around doing this next year and making money.