Ladders are fine, in fact I think it is the best way to go, at least to begin with.
There are safety issues with them of course, and they are increasing all the time, ladder work of any description is slowly being marginalised.
But from a window cleaning perspective I think you are way better learning the tradition style of window cleaning first, build up your round, hone your skills, get your price structure right and so on.
Even WFP, you will still need trad skills, all WFP does is remove ladders from the equation (mostly)
Once you have aquired some decent, basic trad skills, then is the best time to look to move up to WFP.
If you've not worked off ladders before, get some training by someone who has, and understands safe practice.
Ian