Are you happy with the windows that were installed? Are you going to be able to match them with another contractor?
As to what's fair on the payment, did you receive an itemized quote for each window? If not, I would request one that shows the price you were paying for each window installed.
What's installed was fine-SoftLite Imperial LS. I can't get the rest in Soft Lite. I have no idea if I can find another brand that will look acceptable with the SoftLite, at least there aren't any too close together.
I didn't get a quote broken down by window, but have asked for one.