We have several different "types" of properties to include traditional single family rentals, one multifamily rental, lease to buy options with tenants who hope to buy from us, two short term rentals, and some agricultural farm land that is cash rent. 

Option 2: Private LoanIn this option, a promissory note is written for my partner to loan me the down payment amount (20%/$46K) for a 2-5 year term at a 10% interest rate (details are still up for negotiation - are these terms reasonable for this kind of deal?).

Specifically, we're exploring whether constructing a duplex and triplex or two duplexes would be the most profitable option.

Once the home is permitted it will significantly open you up to more lending options without any cuts in value or LTV. 

The buyer definitely owns the property, otherwise it is not owner financing, it is some sort of lease or option or a combination of the two.

We ruled out real estate and stock/ERF options. 

This is not to say this is the only successful method of real estate investing, but as I'm sure you're well aware, with current interest rates and overall market conditions, sourcing and acquiring LTR deals is difficult unless you're going off-market. 

We're looking to raise money for a down payment which is why I considered the line of credit option.

@John Clark, please provide the legal source for that “implied covenant”.  

New construction is certainly a viable option but I am seeing people have great success with the renovation of existing properties.