Since we typically camp on the boat for a week on LP trips, we vac seal our small, SMB and walleye from the first 4 days or so and freeze them in a 15 qt Engel. Fish caught in the last three days go home vac sealed but not frozen because we lack freezer capacity. All our home bound fish are frozen within 3 days, which a really smart chemist once convinced me was the max for bringing unfrozen fish home. It helps that we can still partially freeze a bottle of water by putting it at the bottom of the ice chest on day 7, so unfrozen fish get fairly firm. Three points to consider:
Package for consumption. Our packages weight 3/4 pound, just right for the two of us or one person with leftovers. We guess how many fillets should go into a vac bag, put the vac bag unsealed in a grocery store bag and weigh it with the fish scale. You get pretty good at guessing 3/4 pound. I make bags at home to save time on the water.
Work fast in hot weather. We clean fish at least twice a day. We knock them out, cuts a gill and lets them bleed out. We fillet the fish and have them in zip lock bags within 10 minutes. Once we are anchored for the night, we vac seal without the fillets warming much. The better we handle our fish, the better they taste.
Spring for the best vac sealer you can afford. Over several years we worked our way from the cheapest to the most expensive "commercial" Cabelas sealer. We go through about 12 rolls of bag material a year, and the cheaper units just didn't last and some didn't seal reliably for us. We've been satisfied with the current unit but when it goes, and I'm expecting to outlast it, we'll check out the Weston.
Like in the Spanish Inquisition, there is always another point to consider. If you are buying a freezer and have the space, power and money, get something bigger than 15 quarts.