You could use the sale of your primary and the sale of your investment property to fund the purchase of the land and the beginning of construction. 

I also have some cash reserves that I plan to dump into a contingency fund for each unit. 

The Strategic Neighborhood Fund is pumping money into key areas, and it’s making a difference.

I'm still in the process of finding an alternative solution but I thought I'd leave this here as a warning for others looking to make a decision.For reference, I'll just post their email response to me here:As we review your inquiry, we would like to remind you of the following key points from our Terms of Use:In no instance shall ShinePay be liable for any of the following:"Lost revenue from service interruptions.Lost revenue stemming from delays, malfunctions of any product.unauthorized gains access to your account or due to shared passwords or if your password is hacked.Destruction to properly, places, or personal injury resulting from the installation, misinstalling, or misuse of any product.Lost revenue from entering the wrong account number for ACH or other bank transfer or money transfers or due to any delay in receiving funds.Damage to your structure, machines or car resulting from use or installation of our products.Any funds collected that are paid to a person that does not own the property.Any harm from defeating the lock and technology that controls the lock to a device.Failure to properly service any product or machine."

Spreading funds across 2-3 properties could provide diversification and steady cash flow.

However, you could look into a “construction exchange” where the funds are used to improve a new property acquired through the exchange, but it must meet specific IRS rules within the time frame. 

It would be tough to rely solely on our own funding.

If the answer is yes, then it's a no brainer to make minimum payments on your 2.8% interest rate mortgage, and use the funds that you would have paid extra to pay it down faster, to either invest in more real estate, the market, or anywhere else where you can get a ROI > 2.8%.If the answer is no, then feel free to aggressively pay it down as fast as possible, to become debt-free faster, and just have a large amount of money in savings or to splurge with.The bottom line is that your 2.8% mortgage is GOOD debt.

We’re fortunate to have an above-average income and live well below our means.This summer, we’ll be moving to Detroit (PCSing in August), and we’ve saved about $120,000 to invest in addition to having funds set aside for the home we’ll purchase in Detroit.The reason I’m posting is that I’m struggling to decide how to best allocate the $120k.

Personally, I advocate for a long-term investment strategy and would recommend investing the funds, provided you are comfortable with the expected return on investment over time.