There are a myriad of ways to go about the space, so maybe in the next 6 months you define your first strategy and work to execute on it.

I like this idea as I think it would give me a behind the scenes view of key financial aspects of investing. 

To ensure I navigate these legal aspects correctly and make informed decisions, I’m looking for recommendations for a knowledgeable real estate lawyer or legal entity in the area.

The zoning will define the permitted uses (this will tell you if you can have an RV/Boat storage there) and it will define the density (this will tell you how many tiny homes you can add).You'll want to make sure you don't conflict the existing duplex to a new use or mixed use where you might put the existing use out of compliance. 

The biggest thing we started doing after our first 2-3 flips is focusing on the higher-roi aspects such as kitchens and baths, and then doing "just enough" for everything else. 

What other aspects should I keep in mind and look out for in a property of this age and condition?

Great place to learn about lots of different aspects of REI.

The answer should NOT be a re-wording of what you defined above. 

@Adam Guymon here are some questions that hopefully point you in the right direction:What do you define as a "deal"?

This year I have also hired a bookkeeper at $50/hour to take care of the rental aspect of the financials.