You don't have multiple income streams like you would with multi-family The key is having the right local teams in place.

3) since we will use a local property mgmt firm for marketing / bookings / rent collection, What business is the LLc in and what income and expenses do you report as those of the LLC (vs what do you maintain personally)?

Purchasing your primary with this money, unless it produces income, will likely cost more at the higher interest rates of today vs what you have as a rate on this property.

I've applied for a conventional loan: 3 units, owner occupied, NJ, 5% down.I have enough W2 income to cover the loan and additionally, there are two units rented already. 

NO tenants, no repairs, no closing costs, no rent control just passive income for putting your money in a CD. 

Diversity the way your income is taxed. 

Also maybe turning it into a two family home to maximize rental income is an idea.  

I think you may have very well narrowed down my strategy choices down to one of three; the BRRRR method (although this might be too much to start with for a newbie), the live-in flip that you mentioned (probably the most practical as I've been part of many different projects in the construction industry), and a combination of house-hacking/live-in flip (probably the most rewarding with a potential to swap between units as I finish one in order to bring better rental income).

Right now the rental income covers most costs and I’m going to be paying 600 a month of my own money. 

Following is the income for all the unitsRentsNew Rents Expenses Unit 1: 1800 sqft $ 975.00 $ 1600Insurance $ 6,000.00 Unit 2: 1100 sqft $ 900.00 $ 1100Taxes $ 2,728.00 Unit 3:  1100 sqft $ 925.00 $ 1050Sewer Charges $ 4,800.00 Unit 4(Apartment): 700 sqft $ 700.00 $ 850Vacancy $ 4,000.00 Total $ 3,600.00 $ 4,600.00 Repairs $ 2,000.00 Yearly Revenue $ 43,200.00 $ 55,200.00 Total $ 19,528.00 Mortgage Interest Only/m$1,460.00$1,460.00Mortgage Interest Only/y$17,520.00$17,520.00Current Income Projected Income Net Operating In $ 23,672.00 $ 35,672.00 Cap Rate4.30%6.49%Cash Flow With Int Only $ 6,152.00 $ 18,152.00 Cash invested $200,000.00$200,000.00COC3.08%9.08%What are your thoughts on this deal?