Hi Edson!
I have some experience with this, but in illinois.
I once bought a property that had a smaller house in the backyard, commonly referred to as a coach house, that was called a legal non-conforming structure. This meant that it was not code conforming, but they wouldn't force me to knock it down since it was already there.
That said, because it was non-conforming, should it burn down or something like that, the local municipality would not allow me to rebuild it. For that reason, the bank wouldn't loan money against it. I had to value the property based on one house rather than two. They also would not count the income from that property in my dti.
So all that to say, the adu conversion is one issue, and unfortunately I don't have a ton to offer there. But what really caught my eye was the zoning issue. It may be okay where you're at, but do a lot of research on it. Sometimes you can buy a property and solve a problem, but other times when you buy the property you merely inherit it for good.