Start with RE text books, like the Principles of Real Estate.

I don't understand how this is more beneficial than just paying more towards the principle every month since I would have to pay interest on the HELOC money and I don't have to do that when I pay extra principle out of my pocket.  

Co-sponsors - This is a team sport, so you would want a partner(s) that has complimentary skills to your skill set.  3 things your team needs to be really good at to be successful:  Sourcing deals, raising capital & asset managementIt helps to have a co-sponsor who can serve as the Key Principle to be underwritable for your loan (depending on the size of the deal)Someone with experience and a proven track record of success syndicating multifamily dealsattorneys well-versed with syndicationI would pay attention to what the attorney's say when you are interviewing for your legal team. 

I'd rather capture as much cash flow as I can and if I decide to pay the property off quicker I'll just put more toward principle or if I decide to use the cash flow for more properties I have the option to do that. 

I personally also really liked Power House Principles by Jorge Perez.

I would think that the "buy the worst house in the best street" principle applies everywhere.All the best.

Principle only?

make sure you're talking about the same terms.P&I (principle and interest) is your actual debt servicePITI (principle interest taxes insurance) is the REAL payment you make each month.P&I for a 419,000 w/14,665(3%) down @ 3% for 30 years is: $1704 PITI will be that plus $228 (the taxes your provided / 12) plus your insurance. adjust your figures accordingly, I used what you provided plus a guess on the rate

I’ve bought nearly 2000 apartments, $100m of deals as principle, and never heard of this. 

Keep in mind with the terms we have, we're returning 100% of the principle to investors by end of yr2.