Welcome to the forum! I'm a Mainer as well and have learned a great deal from the folks here. I'd be happy to help you with whatever I can. New England fisheries offer some unique opportunities as well as unique challenges.
It sounds like your goals and the original goals of the property align with each other, which should be an enormous benefit for you. Rather than trying to fit a square peg into a round hole, you should be able to instead get a good survey of what you have and get to work on the inevitable maintenance that has been neglected until it fell under your ownership.
In Maine, you need a stocking permit to add fish to your pond. In fact, it's illegal to be in possession of live fish (except bait) without one, even if they are in your boat livewell as you are fishing. Once you have a stocking permit, you can get trout from a few different privately owned hatcheries in the state. They should offer rainbows, browns, and of course brookies. I love the idea of having landlocked salmon in my pond, but I believe that the only hatcheries raising them are owned by the state and they aren't selling fish to mere mortals like us. Maine is also the only state in which it is illegal to stock bluegills, even though they are in most lakes and pond throughout the state. Thankfully that shouldn't impact your goals.
For what it's worth, brook trout have the potential to spawn in a pond environment, so if you want to consider a potential self-sustaining population of fish, they are probably worth your time. There is an article in a former Pond Boss magazine about how to create a spawning bed for them. If you call the PB Magazine office, you can buy a copy of it from them. I have learned that trout fry do well in trout ponds, but will likely become snacks in ponds that have warm water species in them (such as bass, perch, etc.)
Data that will be key before getting started with renovation will be getting a positive ID on your current fish species. If you are unsure, the people here are wonderful at helping identify fish if you have clear photos of them and can upload them here. I would caution you from using social media groups, as the "experts" there likely know less than you do. Fishing should get you a good sample of the sunfish (species and sizes) but you'll need seines or minnow traps to get an understanding of the rest of your food chain. Trout are opportunists, but tend to prefer bugs to fish prey so seining the shallows (particularly in weedy cover) should get you an understanding of what your ponds have to offer for aquatic bugs.
Other data that will be helpful will be confirming depths, getting dissolved oxygen (DO) readings at various depths (you can order test kits or a meter for this and it should be greater than 5ppm for trout), temperatures at the surface and temperatures at the deepest point where you have 5ppm or greater DO, Secchi disk readings to assess water clarity, and a comprehensive water chemistry analysis. The one done by Texas A&M University is the best that I'm aware of and is reasonably priced.
Good luck with your project and keep us posted on here on how it's going. Feel free to send me a private message on here with your contact info as well if you'd like to keep in touch outside of the forum.
