Moose are not hard to kill. Shoot what you shoot best, but longish shots are likely, but my last one was about 65 yards. Sight your gun in with whatever is on sale, then try a box or two of different premium. Moose are a big target, even aiming small. Find out from the outfitter what the terrain is that you are going to be in, for the best type of footwear, bring good rainwear and good binoculars. Ask if his camps have mattresses or foam pads....a lot of the back country camps just have eggshell foam, which isn't the greatest. If so, bring your own thermocell inflatable mattress to go with it. Sleeping on hard boards can really put a bad spin on your trip if you cant sleep. Be sure without excuses that you also spend range time at 2oo yards. We brought 3 100 quart coolers apiece for our meat each. Depending on wastage (which can be quite high with field boned meat) we had about 300 lbs before the butcher trimming, with about a 25% loss there. Find out ahead of time if their butcher vacuum wraps, just to be sure.
What part of the island are they on?