steel windows diy design+construction
The windows in the top photo are actually doors. They are aluminum, probably a custom extrusion. 

You will have a VERY heavy window. Your opening mechanism will need to account for that, as well as the structure which supports the hinges. 

The windows in the lower photo are actually made of steel T-section.  Yes, they are welded.  The glass is glazed in using traditional putty glazing (on the outside of the building, very impressive!) However I would use a quality silicone, and a great deal less of it.  

You get sealing by designing for gravity and using rubber gaskets. Trying to do it with steel fitting tightly is going to create windows which bind, get stuck, and are sensitive to tram problems.  You won't knock the window out of tram, but the window frame? You betcha.  

I don't like the screw-in plywood.  You are dealing with heavy windows and it will not hold unless you use a lot of screws.  I would go with metal for that. Tolerances should be not too critical since you should glue in the windows with a quality silicone caulk.  Caulk has no shelf life, it is garbage after a year or so, so don't use old stock. 

Designing windows well is an iterative design. The best aren't good because they're smart.  They're good because they've made mistakes, learned, made more, learned, repeat.