Hey @Anthony F., you're quite welcome! Having those neighbors and family members nearby to help handle the cleaning, renovations, and maintenance is definitely super helpful. I would still check on the availability and pricing of a secondary cleaner in the area though - always want to make sure mom can take a reservation or two off if schedules don't line up for some reason!
I like the pontoon boat rental idea as an add-on service for your STR - on decent-sized lakes, pontoon boat rentals can easily bring in $200-250 for a half day rental or $400-500 for a full day rental, so you could make a tidy little profit off of this kind of add-on amenity. You'll definitely want to make sure you have some waivers put together if you go that route though, as well as getting the appropriate additional insurance coverage for using the boat as a rental. For the kayaks and paddle boats, I would just keep those available free of charge for guests to use if they want; those are definitely great to have as an available amenity though.
The garage loft could be a really interesting opportunity for setting your cabin apart from other STR's in the area as well. Turning the pool table loft area into a full-on game room, or maybe even doing a projector screen with a home theater or video gaming set-up there - that could be a huge selling point for families looking to book a stay with amenities and spaces that will help keep their kids occupied and entertained.
One note on the existing hot tub: having an awesome, well-running, clean hot tub can definitely help you command a nice premium on your STR bookings. Having an older, mostly reliable but starting to show its age hot tub can easily become a liability. If the hot tub you have is hard to keep clean (and keep in mind: the hot tub looking clean is equally as important as it actually being clean), or if it breaks down in the middle of a guest's stay, it can easily cost you in the form refunding part/all of a booked reservation, or lead to your listing getting bad reviews. And in the STR game, reviews are pretty much everything.
Assuming you have the hot tub up and running smoothly though, I'd also take some time to focus on what cold weather amenities you can offer to guests to entice them to visit during the colder months when ADR's drop and occupancy falls off a cliff. Some common ones that come to mind in addition to a hot tub are a cedar sauna (gotta lean into that Minnesota sauna culture - check out Cedar and Stone out of Duluth for some really cool sauna ideas), snow shoes or cross country skis, or even just a nice outdoor firepit area with tons of firewood (you could also include complementary s'mores supplies for every reservation). As I mentioned in my original post on here, the warmer summer months will take care of themselves, but if you want to have the STR operating all year round, the winter months require much more effort to make your property a place people will want to visit and stay even when the weather gets nasty.
Nothing against VRBO, but I would also take a few minutes to check out what listings are available on Airbnb as well. I forget which guest/episode on the BP podcast it was who I heard say this a while back, but in most of the STR world, Airbnb is Google and VRBO is Bing; there are way more people out in the world googling stuff, and not nearly as many binging their search results. Airbnb is also exceedingly easy to get an idea on what 3BR comps in the area are getting for their weekday/weekend ADR, cleaning fees, as well as seeing if there are common check-in/check-out times, minimum stay restrictions, and how booked up their calendars are, especially right now heading into the back half of the busy summer season.
As far as the what kind of legal structures to use for this property, there's so much noise on social media about stuff that just doesn't matter or apply to most people, so I wouldn't worry about overcomplicating your purchase with trusts and holding companies at the beginning. Set up an LLC on the front end and make sure your lender knows your intentions to purchase the property using the LLC, and you'll be in good shape. Having a solid insurance policy which covers your property being used as a short-term rental will be the other important piece to keep in mind.
Hope this advice all helps - can't wait to hear how this project turns out for you!