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I think I would opt for just having some glass cut to fit the openings. build a small frame with trim lumber to recieve the glass and then trim the inside. You certainly don't need the additional ventilation with window openings throughout the room.
Were I thinking of replacing the windows, I would be looking at vinyl. Vinyl windows are relatively inexpensive, maintenance free, and can be custom made to almost any dimension and style, including the odd size of your side lights. Even though this room appears to be a 3 seasons room, I would still elect for insulated and Low-E glass. Low-E helps with heat gain and loss. Insulated glass also helps against outside noise. Insulated glass allows for the addition of decorative muntins between the the glass layers. I think muntins would look good on your style of home with its Dutch roof.
Even if you elect to change the sidelights at some future time, the glass inserts will not have been an exorbitant temporary expense. I have always been amazed at how inexpensive glass can be. One caveate is that building codes might require safety glass in that sidelight location. Tempering of glass can be custom done by the glass company, but you have to have your dimensions exact, as it cannot be cut after it has been tempered.
A few years ago I had a full length sidelight made up in insulated, tempered and obscure glass for less than $200.