I would probably recommend a canoe if half the miles are on water. A UL canoe can be fairly easy portage. On the water it will more than make up for any effort. Wheels are another option, but, I am not that familiar with Boundary Waters regs and portages. The wheels come in two varieties. One is stern mounted like kayak wheels and the other is center mounted. Not sure which would be appropriate.
If you cannot use wheels, with four people, I would recommend a split pack load. Set up in pairs, it is easier to set up one with tent, stove, sleeping bags, cook gear, pads and misc items for camp. This usually ends up to be about 10-12 pounds. That person will also carry the boat, paddles and life vests. For longer than 1/4mile, up to about 4mi, it is much easier to do it in one shot rather than worry about switching off. The other pack will carry the food and cloths for the pair. Often his pack will weigh 45pounds at the start of a trip, mostly food. Each person should have their own water, of course.
If the portages are shorter than about a 1/4 mile, the packs can be left in the boat and the boat just grabbed and carried with the packs in them. This works ok for short carries but can bother your back for longer distances, with the weight off to oneside. Switching helps every 100 yards or so.
If you have a heavier boat, say roylex or or another plastic, I *have* carried them with two people. But height differences can be difficult up and down rugged terrain. Certainly possible, though. This requires good team work so it is best to practice a bit befor actually putting on packs.
You should bring one larger, community tarp. This goves you a good place to stay dry in any rain and out of any winds. Likely a 10x12 or the like. August will likely be warm with cooler nights. You probably need a fire, so a saw is probably something else you might want.
I do a lot of canoe camping in the ADK's, often for a week or two in the St. Regis, Saranac Lakes, Fish Creek Ponds area. Also, the Fulton Chain, Raquette Lake, Forked Lake, Long Lake and, Raquette River, Saranac River...now known as the Northern Forest Canoe Trail(New York Section.) Lots of portages and good canoeing.
Anyway, sounds like you are in for a nice trip!