I would have thought one of the experts would have replied by now. I will tell ya what I know. I would recommend argon or a similar product in all the windows in your home. They don't just block UV rays, they also slow or block transfer of heat and cold. They were just trying to stay competitive with their quote.
The most important thing I would concern myself with is the install. A bad install can make even the best windows useless! Ask for references from previous installs in your area, talk to the customer, go see the windows.
I would also recommend leaving the siding alone. Install the windows as replacement style windows. I've installed thousands and no problems. If there is rotten wood, make them replace it. Also, make them wrap or cover all the exterior wood trim around the window. There is some really good vinyl coated aluminum out there in a wide variety of colors. Don't let them use the baked on enamel or painted aluminum, it chalks up pretty bad after a few years. Make sure they insulate any areas that will be void between the new window and the old frame.
I'm not certain that new windows will resolve condensation issues. Sometimes, new windows can increase condensation on the windows. New windows do not reduce the amount of moisture being produced inside your home! In fact, your old windows are more than likely allowing more moisture to escape from your home than your new ones will. Don't cover your windows with heavy drapes and run the ceiling fans often. If you have condensation problems after that advice, then you probably have a moisture problem in the house. Buy a humidity gauge, keep it around 40% with a de-humidifier if needed.
Good luck with the project, hope that was a little helpfull!