My mortgage broker said that if both loans closed on the same day, the debt from one would not be counted in the expense-to-income ratio of the other.

COUNT ME IN THAT GROUP.  

My gross commissions will count toward my profit share so my brokerage expenses will be shouldered by me and not shown on our partnership costs.

Rent absolutely counts towards income in their DTI calculation.  

I have a good understanding of the rest of the process and don’t have any problems with the collateral portion of the loan, but I am concerned that my DTI could give me problems depending on how much rental income the will count/ what expenses they add to my debt or subtract from my income.

Your total expenses are 33% not counting PI. @ 50% of rental income you will have $675 to cover a debt payment of $809 a month.

I'm not exactly sure how it all works out but I wouldn't count paying down principal as a valid way of compounding money.

My lease does say they have to give me written notice for important stuff and that text message does not count as written communication to me.

Studying and doing research on RE also counts as taking a step toward that goal.

Count me in!