A person starting out with little assets and not much to loose should not be set up with the level of protection as somebody with 100 units.

Doesn't matter the strategy, location, or unit count.

Not sure how that would work-there is the fact that it could be a legal basement suite sharing utilities or a separate unit. 

I recently purchased a property that includes a 3-bedroom, 3-bathroom main house and a pool house that can be converted into a 2-bedroom, 1-bathroom unit.

They have some low down payment 1-4 unit investor programs that can reduce the cash needed (equity line amount) to close.

Tenants are in both units.

If your unit is larger than 2 bedrooms you will probably want to utilize a fluff/fold service unless you have large commercial laundry machines. 

Obviously, I have no intention to start investing in large apartment complexes (Anything larger than 50 units) or incorporate LPs, but curious to hear everyone's opinion on sensitivity tables along with using equity multiple figures.

Is it worth the effort to build another 12 units on the same property in this market?  

And correctly..you cannot co sign as a primary if it's occupied..2+ units can sometimes require larger down payment (as you've found) another option could be to access equity against another property..check in with @Joseph Chiofalo for potential lower down payment options..might be able to get to 15% down..Good luck!