Dining room table size

I'm planning to build a dining room table (rectangular). 80% of the
time it will be used by 2 people, 15% by 3 and 3% by 4 and 2% by 6 (I
hope that adds to 100). This means that seating 6 can be "cozy".

I'm thinking of a drop leaf on one end. I could go with the leaf up or
down for 4. I'd prefer not to go with a removeable centre leaf - I'd
rather deal with two pieces of the top rather than 3 since I'm going
to be banding the main field with some trim and a similar treatment
for the leaf - plus I don't want to have to store it.

Any suggestions as to dimensions? Where would the legs best be
placed? At the corners of the main piece, or inset? I could go with
square - a bit bigger than a card table, and something around a 24
inch leaf, but that sounds too unstable since (seating 6) 3 people
would be eating off the unsupported leaf.