Wow...are you sure a question like that doesn't require a site visit? Seriously, if you don't need coverings for practical reasons, don't bother as the room is beautiful. if those are single glazing, you might wish to have roller blinds fitted against the window and hidden by trim work painted to match the window trim. You would lose a few inches at the top but a talented trim carpenter could make them look almost like a part of the window trim. I could see custom made radiator covers that would mimic the wainscoting would turn those obstructions into a desirable feature. For the top use the same profile and dimensions, at the same height, as the window sills. Columns on the ends and probably three panels of approximately same proportions as the existing ones across the front of the radiators would work well. Do some research on radiator cover design as you need to have good air flow coming in from the bottom and exiting at the top and a properly designed cover will actually help, not hinder heat distribution from the radiators. Despite the term, more heat comes from convection than radiation and channeled air flow will increase the heat transferred to the room. Let me know if you need a link to info about radiator cover designs

They don't both face the street- here let me show you the proximity/positions of the rooms (hopefully this works I've been having trouble uploading photos): should they still be dressed the same? I am not at all opposed, it would just raise more questions for me if I bought the same treatments: ***Is it OK to just do simple linen drapes over such a big window? How many panels would I need? Would I need wide panels?

We don't have room measurements so these are general ideas to consider. Shift the furniture and rug toward the window so you create a "walkway" along the stair rails and between the kitchen(?) and the area with sliding glass doors. You said the furniture is temporary so working with what you have for now: Remove the recliner. It's a space hog, another hard surface, and there are too many chairs that make everything look choppy. Move the loveseat perpendicular to the window and place your end table next to it so it barely touches the wall. Place your velvety red (swivel?) chair in about the middle of the window. It's low which won't block your view out the window. Move your light tan and peach chairs where the loveseat is now but float them off the stair rail for your walkway. Put an end or cocktail table in between. Consider a console to the right of the fireplace and place the tv on it. The little cubby in the corner has potential for a set of small chairs or a table with chairs that can be moved to the main furniture grouping when you need extra seating. Again, these are spitball suggestions so you can see how you like the flow, spacing and function. Measurements are critical before you purchase any furniture and of course, you'll want to choose artwork and accessories that work with those selections and give you the softness you want. What is the area behind the sliding glass doors? This shows a walkway behind the two chairs:

I like the table you have in the graphic- kind of breaks up the space in a nice way. And would also be handy to use from the laundry or the fridge side. Considering the utilitarian nature of the room, you might want to keep it fairly simple with blinds or shades rather than using curtains. Keep the ceiling basic with a white tone. Depending on what kind of crafting you do, you might want that room to be as basic white as possible so you aren't throwing color on your projects. You might want/need to bump up your lighting too.