Brettfelouzis, then the size of the light should be between 20” and 24” long. You could get away with 20” I think. Here’s what I did:: took some painter’s tape and marked out the lengths of the lights I considered by the door. Then I knew which way I was leaning. The “heaviness” of the light plays a role I think, as well. The more metal there is, the more presence it has and thus is visually heavier and in such a case, I would likely choose a 20” option. This is an example from my garage (my front door has a pendant, otherwise I would show it), these are 20” long. I would have gone longer but we couldn’t find any we liked. In the end, you just have to try the light out and if you don’t like it, return it.

I think black/charcoal trim will be too stark of a contrast. I would do the sage green that you posted above with the bottom "white" of your paint samples, which looks like the softest white...and closest to all of your inspirations.

I don't know how you can put shades on triangle-shaped windows. The previous owners of our house had a film applied to the south-facing windows that are high up. Thank goodness because as you can see, all that light changes the color of your floor. No point in refinishing the floor if it's just going to get bleached again. There are numerous brands and dozens of colors of stains available. If you're using a contractor they should be able to provide samples of the stains they use. Every contractor has a preferred product. If you're DIY, just like paint, you need to test stains on a sample piece of wood that is the same species as your floor. Hate to tell you, but almost anything is going to be out of fashion in ten years and no one has a crystal ball to tell us what is going to be "in" in ten years. The only thing I can tell you (because I am old enough to have seen several iterations of what is in and out go by over the decades) is that fashions in floor colors cycle back and forth between dark and light. They change to stimulate sales from people chasing the trends. So suit yourself and chose something that will work with your furniture, and also the wall color since you've done that already. The only thing I will say is definitely do not go gray. That is definitely out and may not come back for decades. Personally I like to go middle of the road brown and skip all the flip flopping between light and dark.

"considering medium brown/weathered oak chesnut/weathered oak" Isn't that what is in your second photo? You say "my flooring guy is pretty useless coming up with combos on his own", but it looks like your second photo shows he is providing what you are asking for. Your top photo is not "medium brown/weathered oak/chestnut". I think the flooring guy is giving you what you asked for, but what you asked for is not what you actually want. Show him your top photo that you posted here. Here are photos of chestnut stain on white oak and weathered oak stain on white oak (a much more gray finish than it sounds like you want). So you need to give your flooring guy the correct instruction of what you want, and not blame him when you do not.