Two shop/warehouse properties with 6 units each and a self-storage facility that has a small commercial building with a business in it. 

This is causing me a lot of stress, to be transparent.I'm starting to consider going more passive and talked to two possible syndications - one an apartment building and one who has multiple investment strategies, apartment buildings, car washes, storage facilities, and a debt fund with 6% to 8% return (depending on how much you put in).

SAN ANTONIO & SURROUNDING AREAS & Throughout TEXAS:I concur with Chris’s markers and assessments within his post.As a Real Estate Investor and Realtor, as well as a Self-Storage Property Manager I can tell you this market is extremely hot.

Needing some advice in calculating the viability of building a mini storage facility on a commercial vacant land.  

Then you have your separate addendum of "House Rules" which spell out what exactly are common elements (Kitchen, Hallway, Bathroom 1, Back Porch, Laundry Facilities) and any specific restrictions regarding use of each (no laundry between 10 PM - 8 AM; clean your dishes before leaving the kitchen area; no storage outside of your personal room; no pets; electrical usage restrictions in the room if any; quiet hours 10 PM - 8AM daily; etc.).

I know people with hundreds of SFHs and that has worked for them and I know investors with only large multifamily.Looking in from the outside everything will sounds amazing STR this, storage that and in the end you need to figure out if you even like it and what you like about it and then scale.Life insurance can be a helpful vehicle but you really just need to make some good money in whatever you're doing and show a level of competency so that people will give you money to be an operator even if that person is yourself.

With limited funds, you can also look into vacant land and rent spaces for RV and Boat storage in the area. 

I do like the software/apps that allow for document storage for receipts and other business expenses/paperwork.

But as you underwrite deals, you will always be able to hold the basic structure in your mind, then work the details on each deal in a spreadsheet that you can easily build yourself.Basic rental income and expense summary:Rental Income from all units, also called Gross IncomeLess Vacancy Factor (typically 5%)Equals Gross Adjusted or Effective Gross Income (has various names, but this is what I call it)Less Operating Expenses and ReservesEquals Net Operating IncomeThis fundamental formula applies to all income producing properties, apartments, office, retail, self-storage, etc.

Storage units.