The only problem is the house is zoned as a single family and they have added 2 units behind the house without zoning to multi family so several banks are unwilling to finance.What options do I have here?

It's hard to screw up a single family purchase, but as you expand your portfolio the financing choices you make now and along the way matter.  

The problem was that after I made that down payment of about $45,000, I had very little money to keep expanding.I had to use multiple lower money techniques in order to grow over the years including:-401K loan for down payments on three properties-FHA owner occupied 4 plex with 3.5% down-Conventional mortgages with 5% down on 2 single family homes that I owner occupied and later turn into rentals-BRRRR method on one home to get all my cash back and buy another propertyThe next thing I'm doing is either refinancing or selling a property in order to get way more units.

If you are renting out single family houses I recommend a 3/1.

When I'm in a SFR, I house hack by renting out the additional rooms (albeit I'm single). 

We will be purchasing another long term rental (single family) before the end of the year and plan to BRRRR properties until level 1 of passive income is reached (7-8 years/10+ properties).

Someone could be worth 50 million but if they have no guarantee or a single entity remote LLC it is worthless.You could have all that other stuff and they could simply walk away and keep running other locations of their businesses.If they are a large corporation you want to see if they are credit rated and then if investment grade BBB- or not.

(not so important but if they only require 15% down on a single family home that is usually a good sign that you are working with a flexible lender) Can I change title to my LLC?

Single Family Home. 

The plan is to sell my single family and buy a 3 or 4 flat.