Same pump as my 16 cruiser. West Marine has been out of stock on most Rule's for at least the past two weeks. They are blaming the supplier. One thing you need to watch for is the outlet size. They differ between the sizes. The Rule 1100 is 1 inch.
Having just purchased (yesterday) my C dory, I can't really answer your question, but I know they state 700lb limit for people and gear. Given that, I'd say safely 3 people and a cooler!
Todd