I am trying to discover the real way to earn my family some additional income in real estate, either through flipping, or developing rental properties. 

It is a triplex, I ran the numbers through the BP calculator and they appear to work, however asking for additional advice never hurts. 

Additionally, we are focusing on single family homes in Bergen County, NJ 

The Roth portion of another qualified employer plan like a 401k, 403n, etc can be rolled over into the Roth portion of a Solo 401k.The solo 401k does provide the ability to do an in-plan conversion of tax-deferred funds to Roth status (with the corresponding tax implications), and allows for generous new Roth contributions up to $18K per year.A Solo 401k is exempted from Unrelated Debt Financed income taxation (UDFI) when using mortgages to acquire real property.  

If you acquire a property, from a Wholesaler, once the property is rehabbed and ready for the Retail Market, allow the Realtor that provided you the zip codes, to list the property for sale.

This project is essentially a complete gut that will include addition of roughly 700 SQF, new roof, siding, landscaping, privacy fence, hardwood flooring installation, interior re-design into an open concept floor plan, upgraded kitchen with granite counters, new cabinets, stainless steel appliances, etc.

It's taken about 45 minutes minimum to add each new property we acquire and older ones longer.

My first property was financed via conventional loan and I will rent it out if I am able to acquire a 2nd property via FHA loan. 

Or at least have to have one or the other to be able to acquire property?

At 80% LTV, this would give me a loan of $68k, enough to pay back the Home Equity Loan and essentially acquiring the property with only $2000 (Plus holding costs of Home Equiity Loan + extra interest to money partner). 85% LTV would be really nice as it would give me more wiggle room with extra unforeseen expenses/costs and perhaps need no money out of pocket.