Buy a set of ladders,mop,squeegee,bucket on a belt,scraper,bucket,A frame,scrims and cut up some old towels.
Buy a escort van or similar size get a good roof rack fitted and summat to secure the ladders.
Print some leaflets,and take them door knocking-Simply say-"Hello,do you need a window cleaner??" If door not answered post a leaflet.
Absolutely no point at all in starting up with WFP-far too much outlay.Start small and work your way up.
Most of all,be confident in your approach to it.
HTH