I agree with Alex's definition of an accent wall. I have one in my LR which frames my fireplace and is a focal point for the room. Another rule of thumb is that it is a single wall in a room and not multiple walls. However, the way you are describing just bumping up the intensity of the existing wall color I agree is not really an accent wall. With that in mind, my vote would be for A (but excluding the DR walls). What you have described reminds me a lot of my local Pottery Barn store and it is a very good look and does indeed add visual interest to a large and open floorplan without drawing overmuch attention to itself as would be the case with a true accent wall. You should also take into account the amount of light that your various walls are subject too--since that also has an impact on how the wall colors are perceived. In general the stronger the sunlight a room received, the more washed out a color will appear.

Take a look at greatbigcanvas.com for large artwork. Not sure of the biggest size they offer, but it would be a good, affordable place to start looking.

As for what comes first, the art or the chandelier.  Not sure, but my first thought is that the chandelier position will be based on the table, meaning the bottom part of the chandelier will only be x to y inches above the table.  Heres an article that helps explain range and how to adjust based on ceiling height... https://www.tidbitsandtwine.com/chandelier-height-above-table/#:~:text=For a 9-foot ceiling,in proportion with the room.

if you really love grey, go for it. but I really think that grey toned hardwood floors will never work with a warm toned ceiling. so mockup #6 would be the best bet. what's giving me pause is how it looks against that one wood accent wall. it's so hard to tell how it's really going to look in real life. DIY software is helpful for narrowing ideas down, but it's never going to get the color exactly right. note: I'm not an interior designer. I'm a graphic designer with a good eye. I can help people with ideas and examples when they feel stuck, but by no means am I qualified to make strong recommendations. you have some really big decisions here, and you might want to hire a pro for this! if anything, they can do mockups that are much more realistic so you can get a better sense of the outcome.