Lots of brilliant advice here.... if you are going to go WFP dont get to carried away by all the electric reels and gizmo's....& flashy stuff.
Once you have your water in the tank.... it's just a matter of having that water get to the top and out the brush head.... Get a controller, a decent pole(slx of some sort is fine), 500l tanks seem to suit most people for a good days work... Most people think people will not accept wfp, most people don't really care tbh... Explain it but don't over explain it....its just window cleaning afterall :-)
You simply do not need to have the flashest van, all the bells and whistle van system, Versace bespoke window cleaners clothing summer collection , sign-writing and all the gizmo's.... the whole process is pretty straightforward, many peeps like to get a little carried away like WFP is rocket science....
My only main advice is invest in decent poles and lightweight brush heads..... many people started with backpacks and worked that way with a few barrels in the back of their cars for years...As with most things KISS!
Good Luck...
Dave.