You're photos are absolutely awesome and they exemplify why people gravitate toward such beautiful properties even if it means living on mac and cheese for years on end. Really glad that someone who is eager to learn ended up with the title to that property!
The crayfish probably are rusty crayfish. When I was up in Ontario the last time, I noticed you all were inundated with them just like we are. It happens. One of the problems with invasive species is that they simply don't stay put. For this particular species, it's pretty well accepted that the introduction was as a result of sportsmen as opposed to say ballast water from a ship. A fisherman several miles away from you or a guest to the property decades before you owned it could have easily been responsible for the initial introduction and from there they reproduced and "naturalized". If you've got it in you to turn them into raccoon chowder, you might seriously want to consider it. You could probably even toss them into the bottom of one of those canoes and the critters would find them. You too... could become a Woodland God to the local critters.
I kinda figured you had that kind of turtle. It's the description of the beak that gives it away every time. It's indigenous to where both you and me garden and has its own special niche in the environment. That's a species you need to steer clear of. They can get rather crabby (understatement) and mature adults can easily take your hand off at the wrist. This is not a joke and I am not exaggerating to make a point. Hopefully it will comfort you to know they don't move as fast as you and me can move so we can stay out of their way easily enough. The other thing that's nice is they don't go out of their way to go after us.
So you want to learn more about your land, eh? Good for you! Ok, one of the best publications available that I'm sure you can pick up from your library would be, "Lakescaping for Wildlife and Water Quality" by Carrol Henderson. Watch out which publication you pick up as there's a new release out which is the one you'd want. The cover looks like this-
For your situation, I'd even suggest you actually buy this book so you can mark it up and keep it for reference. Just make sure you're getting the newest edition and Amazon isn't always the cheapest-
The next book that would be invaluable to you based on your sincere interest would be, "Bringing Nature Home" by Douglas Tallamy. This is what the cover looks like but again check around for the best pricing-
The above would be another book you might want to consider buying so you can mark it up, dog ear it, stick slips of paper in, and really go at it.
Books that are so well used they are falling apart are almost always owned by people who aren't falling apart.
Again, so happy that land is in the hands of someone like you.