I have extensive knowledge of working with Pinellas county and the city to get your Airbnb in good standing with their codes and requirements, along with access to many tools and systems to generate free analyses for you on any property.

I do think that a few of these big things will require a loan - the paving for that one multiplex is estimated at around $30k and the septic tank issue for the large multiplex would likely be even more.

Give them the minimum required non-renewal advance notice and be done with it.

It seems like you would have the funds required to take the HELOC or just from investments.

Be aware that the lead paint laws require you to delead rental units within 90 days of closing in order to not be liabe for past tenants.

A builder has special requirements when the financing comes from an FHA loan.  

Required down payment is typically 20-25% depending on FICO, property type and level of experience. 

So I require all of my sponsors at this stage to have at least full real estate cycle experience with little or no investor money lost (and the more cycles the better).

The primary challenges would be about the safety of settlement transfer for a physical currency transfer (like gold) and the specificity of timing and valuation of transfer in digital assets. 

Of course, with all things, the answers to all these matters will depend on the circumstances.California tends to have more laws on the books and requirements and restrictions that it can be a good idea to form a CA LLC for out of state property so that you as a CA resident are covered, and to try to have your contracts fall under the purview of CA courts.