I made my own windows 20+ years ago for my shop. 9 double hung windows in the shop and two sashes that swing inside in the loft. I used 6/4 Luan for the rails and stiles. The sash are 6 pane top and bottom. Glass is double pane glass set in putty. .I am a more than a DIY , I am a retired carpenter but this was the first try at making windows. I got information by studying the Anderson drawings .
I have made a few windows in my day but it was before replacement windows were so common. With the cost of lumber today I can't imagine what they would cost in materials not to mention time. It would be easier to replace the whole window with a cheaper wooden one than try and build a sash to fit and it would most likely be a better built draft free window. One other option would be to contact a window replacement company and offer to buy sashes that they remove that would fit the opening. But there is a reason that people replace old wooden windows.
I made several sashes for our daughter’s lake cabin that was built in the early 1900’s. I have the same router and table you are considering. I bought sash router bit set 55-802 from Infinity tools. They have a very good instruction video on making sashes. They were quoted $500 per window from a local carpenter. I made them for way less than half that using 5/4 clear white pine. Nine windows/ 18 sashes. Of course I made them for cost of materials only.😊
Thank you.
