I have an older home with V-groove wainscoting and board-and-batten paneling, and when I've painted have always painted them the same color as the baseboards and other trim. I think it would be really awkward to try and transition from stained baseboard and door casing to painted paneling. Maybe someone else can come up with some encouraging inspiration pics.

I would do one colour on all the walls. If white, definitely something that leans warm and soft like the inspo pics,not crisp. Probably would even keep to the same sheen throughout,depends on the flooring and other trim (including closet doors) in the room. Sounds like the space will be absolutely lovely. Congratulations!

This problem is common when people install blinds or shades on windows. There can be a difference across the space from top to bottom. When measuring for blinds one should measure across the top, middle and bottom. It is also advisable to measure every window because there may be only one where the opening is problematic. Otherwise one could find a blind binds against the trim at some point. Framing lumber is not necessarily straight. Each piece can have a crown, bow or cup. A poorly placed crowned board could cause a bulge or dip in wallboard. A wall that tees into another can also be out of PLUMB or out of square to the wall it butts against. It happens and the trim carpenter has to make the defect disappear. No discrepancy was noticeable until you added the trim.

Accent walls are falling out of favor because they are not really a substitute for all around cohesive architectural interest. It's like wearing one red shoe. Yup. Everyone sees the one red shoe. But that shoe will look much better with another red shoe, a paisley printed shirt with red in it, and a red belt for the pants.