We learned that the windows on the south wall should be different than those on north wall.
Maybe, maybe not. Depends where you are located, the orientation of the windows, landscaping, etc. If you are in a situation where you can take advantage of added passive solar gain, then yes, the south wall would be the spot to do so.
Wood is a feature in the room I would like to maintain and we have discovered it is expensive and limited in availability.
Expensive: Yes. Limited in availability? Not sure what you mean by that... Wood windows are now available in custom sizes and have a tremendous number of options available.
You might also consider expanding your product search to some additional products. The Stanek has some nice performance ratings, but the pocket sill on the double hung is undesirable (channels water, dirt, gunk, etc through the frame). Preservation is an Alside product and does the same.
Look for a product that has a u-value of .28 or lower in double pane, an air infiltration rating ideally lower than .05cfm, and a welded, sloped sill.