My first house came with wood single pane windows. I wanted to make improvements without spending any money, so added extra panes. I carved out rabbets in the frames and set in a second pane of glass.
I found out real quick that the inside paint film needed lower permeability than the outside paint film after the space between the panes collected puddles in winter. Sealed the inside wood surface, and that space dried up.
I also found that, no matter how much effort I put into cleaning the glass, the result ended up looking at least a little bit foggy.
I tried putting four panes of glass into one double hung window. The air space was about 1/4" in that window. One of my sisters put a window quilt on the inside and the wood frame got condensation while the glass stayed dry. Then that heavy window got away from her and smashed her finger.
More air spaces will reduce heat loss even if the air gap is not optimal. And smashing your sister's finger is not good.
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