I've got a similar dilemma with my porch.

The decision that must be made is whether you want a properly manufactured double hung or casement window that is "close" to the existing sizes or whether you wish to duplicate the existing storm windows to fit the available space.

In the former instance, you get a proper operating window with double pane insulating glass. You can add suitable dividers to give the look desired. But, you must reframe the structure to accept these windows. Of course, Marvin would make you a custom fit window for your openings, but, don't ask the price.

In the latter instance, you give up the insulating qualities of a manufactured window and just make a suitable frame from cedar. It's not all that difficult to do and you route a channel for the glass. Get the glass cut to fit and install it with silicone or with traditional glass putty. I made a set of these for a rental house in one afternoon. Due to their size, 4.5' x 5', I opted for plexiglass rather than full window glass. The weight of full glass would have been problematic to remove and reinstall. But, full window glass is preferred for optical characteristics over the long term.

I'm still struggling with the decision for the porch on this house. I love the look of huge glass panes without anything breaking them up...........but, the look from the outside is not with the traditional exterior of a Dutch Colonial.

I'll be watching to see what you find.