Sorry, I must not have explained it correctly. The tender only brings people out and back to the main boat and is used to keep the main vessel on the dive sites 7 days a week making money, not spending 2 days a week going in and out of port. You dive from the main boat, and it rotates around on a set of moorings that each offer great diving. Finding a location may be difficult since you want enough possible dive sites that offer good diving with a reasonable distance so you can easily move every day or maybe even twice a day between sites to keep things changing up.
No worries. When I went back and looked at your post you did explain it correctly, I just misinterpreted it. It would certainly cut down on port costs and fuel consumption. I am not sure how well weekly provisioning would go (especially in rough sea conditions), but it could work.
Not sure what it would cost to ferry people/provisions out to the boat, but it would depend on the itinerary. When we used to do the Belize itinerary and we would have guests and/or luggage not make the port departure (due to late flights, etc.) the local boat operators would charge the airline over $600 to ferry out a couple of guests or luggage to Lighthouse Reef. Nekton or its guests never had to pay it, but these boat operators raped the airlines to pay for transport.