Its a lot cheaper to start trad but WFP is definitely the future. So get some experience first but save up for a good system later.
First of all dave welcome to the forum, what ever the question, there is always someone one here with the answer, so never be afraid to ask, even the most trivial questions.
Also welcome to window cleaning I hope you enjoy it, Why don't you look into the commercial side as well, this will reap you more money.
The reason I have inserted a quote from Vince, is I agree entierly with his comments, you need to have the traditional Experience first, and as vince said the layout cost is minimum.
but use the time while your gaining Traditional skill, to look into water fed systems, this is the future.
Good luck with your new venture.