Renting out the 3rd unit to another tenant and there is a 2 car detached garage that we can rent out for storage.

That is indeed double taxation.If you owned a shoe store, for example, you would buy shoes wholesale, sell them retail, and pay taxes on your net income.

My wife and I focus on both flips and airbnbs, with "infinite banking" as our wealth storage mechanism.  

So i start my career in real estate as an agent and about three years ago I discovered Biggerpockets community that I dicovered that the ways of making money in real estate are basically unliomited, creative financing, storage, flipping, house hacking, wholeselling and much more. 

I am looking to construct a Self storage facility and I am wondering how much I should pay for land.

Look at parking lots, or storage, or flex warehouse, or apartments, or large multi, or office conversions, or small office, or land banking, or hotels, or STR.   

I would like to learn about self-storage investing.

This could be a home with a floorplan that allows you to rent a room, a guest suite, storage area in the backyard, etc.

It has 2 apartments, 2 storefronts and a storage area. 

I've always tried to put myself in their shoes and what I would expect.