typically anyone who says the following are not actual buyers:1.

Sounds like someone is getting a referral fee or some sort of incentive.

Expect rates to be higher than "typical" financing programs - right now, I'd plan for at least 8%+ depending on the whole scenario. 

The cons as i see it include loosing the 2 of 5 year cap gain exception, typically not an ideal rental because the emphasis at purchase was buying a good home for your family and not a rental with optimal return (my ex-home consistently has the lowest cash flow for equity in my RE portfolio), not disconnected enough from the property causes addition angst on damage and may result in over improvement.  

I would echo @Brandon Croucier - the secondary market for DSCR's is super aggressive and rates typically reflect that.

And then also do you typically repay each partner their upfront costs from the profits before then distributing profits?

I typically host single family homes, but have been asked to potentially host an apartment complex of 22 units.

Yes - and even when its out there its typically impossible to qualify (need high rate and high DSCR and typically would have to qualify as a LTR - so almost a unicorn or in a really bad market)

FHA loans typically require the property to be a primary residence for at least one year, so he should confirm compliance with his lender.Once rented, he can deduct expenses like mortgage interest, property taxes, maintenance, and depreciation starting from the date it's available for rent.

That's typically because they have a lot of money and experience.