I agree a rug can make this a simple choice but I do not like mismatched chairs and what size is the space ? Please replace that fan with a proper chandelier once you have decided on table.

Definitely get a rug and possibly try a round dining table. A lot of dining rooms are more rectangular so they don't lend to round tables but this appears to be a good size and shape for a round table. They make for great conversation!

Basically you do not want to have a table and chairs the same color as your floor. If you have a rug you could do that if you are really set on dark wood; however, lighter finishes are currently more commonly found in modern interiors. If you want to have mismatched chairs, I suggest you do this only with the chairs placed at the head and foot of the table. If you do get a rug, make sure it's large enough so that when the chairs are pulled back they are still on the rug.

Spend a couple hours looking at pictures on Houzz to get an idea of how various tables look. Restrict your search to your style and room. If the dining room opens to another room you will want to be consistent with what is in the other room.