The quickest way to see what you can do is to go talk to an architect/engineer and run your plan by them.

It has extra land where we plan add another 1-3 rental units.

I sold because the market there is nuts right now: everything going for way more than it has been trading at over the last few years.

We plan to fix up each unit as they open up and raise rents to market.

@Steven CatudalFor such a small amount you could try to open trade accounts and commercial revolving accounts for your material expenses. 

I'm 16 years old and I'm planning to invest in real estate when I turn 18!

It's possible for certain sellers to fund the sale of a home, so you can buy real estate without depending entirely on conventional financing.It's critical to get advice from real estate agents, financial advisors, and other specialists before making any decisions in order to customize a plan that fits your risk tolerance and financial objectives.

That sounds like a plan! 

It turns out I don’t plan to ever touch the money, I should have invested it in more real estate, but I was a young and dumb sheep. 

Knowing what you're looking for and having a clear plan in place for what you want will surely help.