First off, hello and welcome to the forums.
I want to begin by saying that I believe that both Mike and Tom pose excellent suggestions. Both of their plans involve taking the Voyageur II or Sea Hunter from Grand Portage which is an ideal source of transportation considering that you are from Minnesota. Mike's plan will allow you to save some money if you are on a budget and do not want to pay the extra $13 per person for inner island drop off or pick up (in other words getting dropped off at McCargoe Cove or Rock Harbor/getting picked up at Daisy Farm, Chippewa Harbor, or Malone Bay.) His plan will also let you get a start on the day right away. On your first day, from 10:30am (around when you will arrive and check-in) until an hour or so before dusk starts settling in (provided you stop for lunch and a couple of short water breaks), you'll be on the trail hoofing it away. The only concern about this plan is the miles. However, you do say you are in relatively decent shape and are in your 20's, so I believe, as long as you have nice comfortable hiking boots that are broken in and you are carrying around or under 40lbs each (maybe a little more for you and less for her), I think this trip is very doable even with backpacking experience set aside. However, if you want to play it safe, and there is never anything wrong with that (better safe than sorry), perhaps this is not the plan you want to go with.
Tom's plan is a wonderful plan too. As he mentioned, going with his itinerary will allow you to stay at places with shelters which is nice because you would not have to set up a tent if you were lucky enough to get one. His plan also allows you to do something you are already familiar and comfortable with, that is, it allows you to have a base camp for your first day and to do a day hike to the mines. Perhaps this will be a more ideal way for you to start your trip. It also allows you to see many peoples favorite sites. This is just an assumption on my part, but I think if you asked a 100 people what there favorite site is to stay at, at least 75% of them would either say McCargoe Cove, Moskey Basin, or Chippewa Harbor as their first choice. Tom's plan also allows you to have lower mile days with the benefit of allowing you to be picked up right at the docks. The only concern about Tom's plan is if it is in your budget to play the extra money for inner island drop off and pick ups and if it is alright with you to have to backtrack from Moskey to get to Chippewa Harbor.
I have another plan that you can consider. I throw it out there as another option to review based off of your preferences.
Day 1: Take ferry to McCargoe Cove arrive at docks at 1pm. Setup camp and explore the mines. (No Miles)
Day 2: Hike to Todd Harbor. (6.6miles)
Day 3: Hike to Hatchet Lake (3.9 miles)
Day 4: Hike to Malone Bay (11.3 miles) Take ferry home the following morning.
When people ask for suggestions, I try to give more options rather than opinions until I get a better feel for what preferences they have as hikers. If I were to give you my opinion, my plan might include too many miles, include too little miles, include places you do not want to stay at, include a direction of travel you do not want to go in, include options that cost more money, etc. Only you know what preferences you have as individuals, and therefore, I simply I try to lay out the different perspectives to keep in mind with each option so that you can determine whether or not your preferences align with those perspectives. If they do, then we have found YOUR ideal plan. With that taken into consideration, I think the above plan is also a nice once to keep in mind. Not hiking on the first day and setting up a base camp will allow you to stick with what you are familiar with just as was the case with Tom's plan. This plan will also allow for light miles with the exception of the last day. However, if you are going to do high miles at any point during your trip, its best that they be done in your final days when your packs are a little lighter from eating your initial days supply of food. The nice thing about doing high miles on the last day of this particular option is that the hardest part would be tackled at the begining of the day rather than at the end. The hard par that I speak is the .3 miles ascending up to the Greenstone Trail from Hatchet Lake. You would also have energy from doing a short hike (3.9 miles) the day before and may even be eager to tackle something a little more challenging. It could be a great finale to the trip, and being that you are in your 20's and in decent shape, I definitely think you could handle it. Furthermore, this plan would not include any backtracking over any already hiked terrain. It would also allow you to stay at shelters for most of the trip. McCargoe has them, Todd as one (so a little luck would be required), Hatchet doesn't have them, but the site does have a beautfiul lake to sit and gaze at, and Malone has them. Finally, just as with Tom's plan, it would allow you to get picked up from the dock directly at Malone Bay. I think it is a good option, but again, there are two concerns with it. It will involve a long last day and it will cost more money to do because you will have inter-island drop off and pick up points.
Now you have three options to consider based off of your preferences
![Smile :)](./images/smilies/icon_smile.gif)
One other thing. Something that was forgetten to be taken into consideration was your "looking to avoid the masses" line. If I were you, I would go in May or September. I would suggest October too, but that option is only possible with the Ranger III ferry in Michigan. By going in May or September, now only will you be avoiding the masses, but you'll also be avoing another M word. Mosquitos!!! You'll also increase your chances of obtaining shelters when arriving at campsites eariler and later in the season. I hope all of this information has helped. Let me know if you have any other questions or concerns, or if you would like to elaborate on your preferences so we can figure out what option is best for you or if an option that has yet to be mentioned needs to be considered.