For my recent dining table build I wanted space for 6, but most nights it's just 2. When we have people over we plate up nearby so there isn't a need for platters of food on the table, and I deliberately wanted a longer, thinner table to bring people closer together, like a refectory table.
("A refectory table is a highly elongated table used originally for dining in monasteries in Medieval times. In the Late Middle Ages the table gradually became a banqueting or feasting table in castles and other noble residences")
I built it 7' x 28", and that was fine for 6, 3 to a side, with 28" per person it feels not at all tight to us. Then, due to a marriage etc, we had to start seating 8 by adding chairs on the ends. This has also turned out to be fine, for us it's cozy in a good way. Based on all that, I believe that the minimum for 10 people is 9' 4" x 28". Then, I would add to that depending on the other factors if needed. I also like the look of a very long and thin table and would build it to that minimum myself, clearly others would go bigger.
I would build the table out of Ipe (Ironwood), unfinished. I've got an Ipe deck I just hit with a pressure washer once a year in the spring and it looks fine. Pressure treated wood is the worst possible choice for so many reasons, my opinion.
If you want to see the 7'x28" table I think you can click on the My Photos link, and in one of the photos you can see the Ipe deck a little in the background. The table's on wheels so we can roll it out onto the deck on nice days.