I have a question a friend of mine that owns some property said it’s going to be harder for me to get a four unit next because I acquired a duplex first is this true ? 

There are two people living in the unit, one has signed, the other hasn't. 

But I find the C+/B units have the best balance of income and affordability.  

Layer on the fact you seem to have a small account which suggests you are not getting the same pricing as a client who has many units under one roof where there are greater efficiencies. 

Use your VA to buy a 2-4 unit property and accelerate your portfolio growth.

One that is attributed to the top unit and one that will be for the bottom unit.

SFH rentals -> new construction -> existing & ground up multifamily up to approximately 75 units.

Doesn't sound too great to me; that guy in the video said some complexes have 150 or more vacant units. 

While some lenders can get creative with income and/or don't require personal income underwriting, DSCR lending programs technically only apply to SFR 1-4 units and small multifamily (usually to 10 units). 

If you succeed you will likely pick up more units and it will become consuming.