The door slab can be used for the barn door, but you'll want to remove the hinges and patch/paint them. The knobs could be left on, but realize that they'll prevent the doors from opening the full width of the opening (may not matter to you). And you'll have the latch mechanism that will be extraneous. Here's a photo of a barn door setup we used between a bedroom and bath. We still had normal molding (casing and baseboard), so that wouldn't need to be removed. Your doors will just cover the opening (like they do now) without any overlap. Also, the door jamb will have mortises to full in (where hinges were), an extra piece of wood in the center of the door jamb (don't know the name) that doesn't exist for wall openings without doors. Those could be removed. As long as the above don't bother you, it can certainly be done.

I have light filtering pleated shades on the french doors. (not honeycomb). They are hardly noticeable when not in use.

@Sulsa, what were you quoted for the Anderson? That will help us to know where you desired price point is. I like Jeld-wen and Thermatru fiberglass doors, but not from big box stores- you want the ones sold be independent sellers or local lumberyards. Jeld-wen definitely has the door style pictured above.

Forget British Colonial and forget the valances and blinds. Let's start approaching your coastal dream right now by whitewashing the brick and painting the mantel and trim throughout to match your kitchen cabinets. Paint the walls Sherwin Williams Sea Salt. Take down all the blinds. Do the same with valances and offer them and the petite matching sofa and leather chair on your local FB Marketplace or other online sales site. Get the idea of valances out of your head. Instead install bamboo shades throughout. What are your floors under the carpet? Looks like the landing at the sliders is wood? Is that under the carpet too? If so, unveil it, refinish if needed and plan to use a large sisal rug to anchor the seating area. If you can't afford new seating right now, get a second chair and do white slipcovers on two chairs facing the fireplace. They will be more comfy than that small sofa.