I would agree with you that an 18' beach cat is right if you plan on sailing with four adults. I owned a Hobie 16 for many years. Although it could carry four in light to moderate wind
and sea conditions, two adults was the maximum payload when performance sailing, or when the wind
As far as righting a capsized 18 footer, I would imaging you'd need at least two good sized people. I could not right my 16 alone unless a boat happened by and helped by lifting the mast
tip out of the water to let air under the mainsail
, or by pulling downwind on a rope
tied to the upper hull
. The Hobie 16 manual said that it takes 250 lbs hanging on the righting line to bring it upright. Perhaps the manuals
for the boats you're looking at will have advice for you.