Looking at your photos I see alot of sq's and rectangles. Consider a round table wooden base with glass top. I like the Red chairs. It will flow in your room and it makes for a much nicer experience using it. Using the glass top also will give you a larger table without filling up the room visually.

The table I have currently actually has sides that flip up. However, that leaves no room on the side of the buffet, which is why I'm leaning towards the rectangle. It's also worth noting that there's a wide arch going into the dining room....

Then it sounds like the bench, chairs and rectangle is your best bet. I would suggest you use 2 benches and 2 red chairs.

I feel like the 2 benches might lend a little more flexibilty while the red chairs would add some pop to the room. Here's the table I'm looking at with the two red chairs

How many people will be using the table most of the time? Benches are not that comfy and the ones with the parsons chairs will be the "elite" at the table. :)

It's just myself and my husband most of the time, although we do like to have people over from time to time. I thought maybe some cushions on the benches if needed?

Yeah, Just a shaker bench - this

How about your table with four of the red parson chairs perpendicular to the window? But, have only the parson chairs on the sides of the table. But, go ahead and get the bench and put at the end of a guest bedroom bed for convenience. So, if you have a larger dinner party, you can just bring out the bench to seat more.

Consider looking at antiques that are the scale of a room from that era. Mission style? Maybe an English draw leaf or pub table. Comfortable seats 2-4 for every day and expands to seat 6 for dinner parties.

I've got an antique now, actually - it probably was used as a kitchen table during the early 1900's. It has leaves but when the sides are flipped up, there's not enough room for a person to sit on the buffet side.

This is the other one I'm considering, which might be too big for my tiny space.....

For a small space, I prefer very low back chairs. Tall chairs lower the ceiling visually. Go ahead and get the first table, but low back chairs maybe?? Want to mix it up a bit? These chairs, your table.

Is the rug staying?

Yep, as it matches the other colors in my home...