you have a good plan.

I would take the wood valance off and get a faux roman shade in a pretty fabric. Hang it about half way between the top of the window and ceiling and have it come down to the top of the glass

I don’t think I would remove the valance. Looks likeyou’d see the light more prominently.

I agree with a stationary Roman hung high letting in a much light as possible.

I didn't remove the valance in the image below because the sides of the cuboards would need to have some repair.

The wooden trim piece actually serves a purpose. As eld notes, it allows you to benefit from the light without having to see the light fixture and reduces a bit of glare for anyone looking at the sink from the rest of the room. It is part of the customization of your cabinetry for your space, matches it in wood tone, grain, and style, and is not particularly offensive. You might consider leaving it there.

I get where you are going with the Roman shade idea, but you may not realize what installing one involves. You will be drilling into stained, finished millwork customized for the space to install mounting brackets, tensioners, etc., have a bulk of fabric eating up the volume of that space, and have a lift cord hanging down from it, all for a shade you are not going to use.

If you want color in the space, there are other ways of bringing it in.