If things start looking different, such as 'this is really for my friend' or 'I don't quite have all the money now' or other non-sense, you are not dealing with a principal.

Another down side is that your leverage floats at the same interest rate, if rates increase, all of your properties are effected.The up side is some financing costs can be reduced, settlement costs, but each property still must be appraised, title search and insurance, 20/25% down as to the total loan to value of collateral (TLTV), so in the end, they aren't significantly cheaper, points may be less, that depends too on other underwriting factors.Loan servicing matters are easier, an excuse for a better rate if you can negotiate that, but on your side, your accountant then allocates interest and principal reduction from total loan figures.

In terms of principal and interest payment I would be shooting for 1100/month as my max. 

No investor is going to give you money so you can defer interest and principal to maturity.  

For the same payment, more money is going towards principal.

As long as you are acting as a principal in the transaction, you do not have to be licensed to conduct your RE Investing Co.

While you DO need education, you don't need expensive seminars, at least not now while you're learning general principals of RE. 

Principal gets paid down.

This defines the amounts owed, including a break out of principal and arrearage. 

It seems like maybe $100 a month of the rent is standard to be applied to the principal, and just based on rough calculations it looks like with financing the first few years like 160 would be going to principal for us.