Eandhl, I know the standard "rule of thumb" I was taught by designers was 24" for chairs; personally, I prefer your 36" suggestion. I think "rules of thumb" are often too minimal. I like to err on the side of "graciousness" when I'm able. I would also like to caution that any rug that will underlay a dining table should accomodate the expanded table by at least 24" on all sides. The rear legs of the dining chairs should remain on the rug at all times, esp. when the chair is set back to accomodate seating the diner! When I ordered my sideboard from PD his website was different than it is now. At that time he had an excellent tutorial on round tables and the space they ought to occupy. I don't know if that bit of advice was culled when the new site was brought on line. I certainly hope not because it was very useful. I think allowing 24-36" around the perimeter of a round/oval dining table is certainly adequate for the comfort of diners.

I have a 54" round table that I love. We use it with 4 matching chairs - so I can't really answer your question. BUT I can tell you that finding tablecloths for this size is difficult. 70" is too big and 90" is too small. If you love tablecloths, be forewarned. :) But 54" is a great size in all other respects!

The one thing that I would change, if possible, are the solid doors in the upper middle of the cabinet. Is there any way you could have them changed to glass? I think they distract from the display of your lovely pieces, as the doors are the dominant things, to my eye. It would then give you more room to create a pleasing arrangement, with more variety, while still showing some of your place settings and stemware. It may be fairly inexpensive to have glass added to the existing door frames. If that's not possible, then I think you can display some of your glasses, some of your china, but remove most of them and add other things with more color/texture/interest. You might think about adding mirror to the back of the cabinet (or wallpaper, or other paper for color) for sparkle and brightness. This is pretty busy and too full for my taste, but I like the way they interspersed the china and glassware instead of just lining it up, and have added other accessories for interest:I think this one veers back into store display, but would mix up what you're doing now in a more interesting way. And the cabinets are closer in size to yours. I'd still add some more variety, myself. Maybe you could do something like this on a couple of the shelves and add a variety of things on the other shelves:

After calculating what was written above me, it looks like you can fit the same size table I have in my dining room, which is 42" wide by 78" long with the leaf in. We can fit up to 8 people at our table with the leaf in. I also love having a rectangle table! I have two openings in my dining room - one to the living room and the other to the kitchen. I have a door on the other wall and a window on the 4th. Just place your table in the middle of the room and it will work.