7'3" is pretty big for a casement. When open, that size sash would put a lot of pressure on the hinges & operator. If you are leaning toward casements, and don't mind tearing the old frames back to the studs, then you might want to consider casements with transoms. Most manufacturers have the ability to provide detailed drawings of window combinations, so experiment with styles that might interest you.

OK. you have Caldwell Stainless Steel Sipral balances. Thery are quite commmon in older replacement windows. After a while they fail and have to be replaced. I beleive they are available on line along with the proper adjustment tool. From the sounds they are making they need to be replaced and just adjusted. You figure the size you need by measuring them tip to tip. Find a source and they are EZ to replace. The PorchGuy Here is a link that might be useful: My Album

Sounds like a window with a spring counterbalance instead of just a weight. Some older designs still used cord to connect to the spring, often concealed in the window track itself. Sash weight are not small things about 1.5 inches diameter and 10-12 inches long, and need a decent size weight pocket to operate.

Double hung means there are upper and lower sash and both can move. Single hung, ditto, except the upper sash is immobile. Two windows side by side is referred to as paired or coupled. The act of pairing (or tripling, etc.) windows by adding a molding (mullion strip) is called mulling; for instance a pair of mulled double hung windows, or a triple mulled casement arrangement, and so on. Mulled windows fit in a single rough opening in the framing. When another stud or studs separates the windows, they are referred to as grouped. Manufacturers will mull windows up to a certain size at the factory, but really large units are assembled on site. Trivia: there are triple hung windows, consisting of upper, middle and lower sash, each operable independently. Casey