For a group I think you need to consider the lowest ability in the group--one miserable (or worse, incapable) person can make it miserable for everyone. For me, it's an aggressive trip--10 miles a day is about my limit, and I'm just happy with 5. But I'm not in great shape, older, and enjoy time in camp. And for others a 20 mile day is no big deal. So it's hard to say for someone else.
If you wanted to add a layover day you could substitute Hatchet Lake for Todd Harbor and end at Malone Bay. Or stick with 5 nights, but do a short day from Todd to Hatchet--Todd is nicer than Hatchet, and it's an easy hike between the two. This is assuming you're taking the Voyageur II, which can pick you up at Malone. You could also fashion shorter days and end at Chippewa Harbor. For me, I don't feel the need to say I hiked end-to-end, and have never done it. And I don't necessarily have to have a shower at the end--although others on the boat may disagree

.
I'm sure you'll have a great trip regardless, and as Kevinl said, "Give yourself some time to stare at the water and clouds", and everything else around you!
24: MB | 22: BI | 21: RH-DF | 18: MC-DF | 17: WI-SB-WC | 16: RH-CI-RH | 14: BI-MB | 13: RH | 12: MC-TH | 11: WC-HC-WC | 09: MC-RH | 05: MI-MB-RH | 02: MC-CH | 01: BI-RH | 79: RH