for the living room, yes, One large blind, but hang this blind above the header so it makes a statement, and when it it open completely, the entire window is exposed.

I prefer inside mount blinds, But since you want/need room darkening, outside mount is great.

In your case, another one over both casement windows side to side, but whatever you prefer for the height.

Even on side by side windows, an inside mount with two blinds is a great look... just get lined blinds for room darkening.

Measure side to side where you want the blind to end and top to the sill for the vertical measurement. Blinds.com is my go to for blinds on line, a great selection. They often have great sales, so keep a watch out.

You will not get black out with an inside mount shade. They will always leave space on the side, always anywhere from 1/8"-3/8" dependng on the header used. If your goal is black out you will need to outside mount the shade. Also note that with a custom fabric roman shade with black out liner there will be pinholes where light comes through where the shade was sewn. This is because black out liner is made of acrylic and once punctured it creates a pinhole.

There is nothing special about your casing and architecture on these windows so I would opt for outside mount to get a cleaner look.

There is no reason to forgo full height drapery panels just because you have baseboard heat just as long as the panels are fixed and don't close.

With outside mount you can mount above the window and then when pulled up can have more glass showing. Inside mount will cover more of the window. I like Beverly’s idea of the draperies at least in the bedroom when the can be mounted to the sides of the baseboard heaters.

And the bedroom…