Congratulations on the purchase. This room looks like a great space, and you did a really nice job on the drawing. I suggest you move in and take it slow. You may learn more about the changing light throughout the day and seasons that will impact the design. Part of the 'darkness' may be the previous owners' decor - it's all mid tone and dreary. Your proposed windows may lighten the room, but the arrangement and shape, to me, looks like 80's to 90's (plus added cleaning issues). I can see that it would be a costly installation. I prefer skylights for brightening. The effect can be dramatic in most instances. A very large light rug or light floor refinish would brighten the room as well.

I like the wall of glass you e shown (assuming there are things to look at) but at least triple the budget- the windows will be 10k before you reframe, move wiring, reside, etc. Skylights are awesome but can create glare depending on where they face.

IMO adding the windows will not be MCM but rather 80s so I would do larger picture windows on either side of the FP what is tha on the right where It seems to be a doorway into a kitchen but more like a mirror. I would like to see a to scale floor plan and some pics of the exterior of the house

Instead of trapezoid windows, have you considered replacing the lower windows with two sets of french doors (or sliding doors)? This will allow more light into the room, give you the benefit of additional views, and ease of access to the back deck.

Would sliding doors or picture windows be significantly less expensive than trapezoid windows? It would be nice to potentially reuse the window on the left on the south-facing side near the dining table. The "window" on the bottom right is actually a door that is swollen shut and may need to be replaced anyway with either a door or window). The windows/doors would be facing a low traffic residential street, so for privacy reasons, emphasizing the vaulted ceiling, and for providing light for raised plants (they need to be kept away from my cats), I'm leaning towards the upper windows if they are the same price. Though maybe the privacy doesn't matter as much because there are already lower windows? I want to paint the currently blue walls white and whitewash the fireplace to lighten it, but would be interested in tongue and groove ceilings down the line if we're able to lighten the room enough that they wouldn't make it even darker.

I don't have a floor plan, but here are some more pictures of the house and space (these are from two different listings of the same house). I think the light will be fine in the winter when we lose the leaves, but the house is heavily shaded due to all the trees and all the other rooms and the backyard are even darker so lighting up the main living space feels very important. I'm imagining skylights might be difficult to clean/ maintain unless we trim the trees back pretty severely.