Post all the links you want to buddy
If you're just getting wfp stuff for winter use then i suggest a gardiners clx 27 for your first winter (not too much outlay while you test the water, if you find you get lots of work then next year upgrade to a slx)
Also on the Gardiners website you can buy an adaptor so that you can plug your pole into out doors taps so you can use the customers water supply (or make your own adaptor all you need is a hoselock, pole hose, and the connector to your pole)
Pure water is only needed if you are cleaning a clear, transparent surface. G/s/f will be fine with normal water. Polycarbonate conservatory roofs will also be ok with normal water, but if you are then going to clean the conservatory windows afterwards then you'll need pure (and a system to pump it from)
Pricing, just price on your hourly rate. Personally i like to charge a little higher hourly rate than if i were cleaning windows as otherwise i may as well clean windows as its easier, and i wouldnt be making more money, id just be making the same but for a different service!
I'm sure you can still pick up Upvc cleans during winter, but i'd also suggest that it may possibly slow down like your experiance with jetwashing
Saying that, i expected it to have slowed a bit now but got them coming out my harris