Given the differences in unit specs, this doesn't sound like a typical triplex - is this a SFR which was converted into 3 units? 

If I were to own a home, I'd probably arrange it like: 80% purchase price, and lets say we allow 5% closing cost. 10% can be in a conservative common investment, for example an index fund, easily converted to cash for capex needs, 5% in cash at the bank for quick emergencies.

I have thought about using a converted container that has been adapted for use as a rental space or, possibly a trailer, etc, or even new construction, but I have no idea what kind of cost I would be looking at. 

Convert to over under duplex?

Lastly, you have to get permits from the city to convert an SFR to a duplex.

Whether the loan is renewable or convert to perm. will be in the covenants.If your piece of land to build on has such an amazing location from anything else on the market then it might make sense to do it.    

Why not have the current owner go inquire before you buy and convert the lease to a near term expiration if the tenant does agree?  

There is an office that has a closet and could convert into a 5th bedroom with the addition of a window.  

You will likely find a lot of illegal "3" families homes with finished basements: Union City used to have a forgiveness program where you could legalize your basement without penalty (so, convert to a 3 family--my neighbor did this), but the cost of doing this is quite high, and I'm not sure if that program has continued.

I'd like to convert my first multiplex to a full rental unit as fast as possible and invest in additional properties.