Success usually is a combination in varying amounts of hard work, good decisions, and a some luck.When arbitrage comes up on here, as it often does, I am usually "gloom and doom" playing devils advocate because the OP is usually on an emotional high from watching a YouTube video about making 6 figures overnight doing arbitrage.I started my business in 2016 with a high end arbitrage, then began acquiring my own, and lastly into management. 

Since you mentioned the property needs a lot of work, if you could put in some higher end finishes into the cabin (kitchens and bathrooms), there would almost certainly be a pretty solid base of STR guests wanting to stay there - almost without exception, every modern STR cabin in Minnesota and Wisconsin that I've seen are all doing tremendous numbers.  

I’m considering using materials such as wood, PVC, conduit, or metal pipes, combined with canvas, tarp, or plastic for the covering.

Bars will be on the windows (crime reference above).Don't be surprised if your cheap purchase costs that much or more to repair as your repair costs will be much higher than a home built with more modern materials, such as in the 1940s-1950s.

The other units rents would be the only way to qualify at the $700-$800k range and then force appreciation with modernizing one of these aging properties.

The other units rents would be the only way to qualify at the $700-$800k range and then force appreciation with modernizing one of these aging properties. 

Equity raised, debt, or a combination?

In the next few months, I'll have:$260,000 in savings$100,000 in equity in the loft$355,000 outstanding on the houseShould I sell the loft, use the equity, and combine it with my savings to pay off the house?

Modern floor plans, modern mechanical systems, well insulated, generally separately metered etc.

Landlord friendly and low property taxes combined with how close it is to CA it makes visiting properties and building a team easier.