It's difficult to predict which angle of the deal is important to the other party, but be prepared for some give and take to make sure everyone feels like they are getting a good deal.  

@Chukwudi Motanya if you have the ability to go fannie/freddie for your investments, you'll definitely get better interest rates and less (or sometimes no) fees. fannie/freddie cap out at 10 financed properties, though, and they will qualify you based on income and ability to repay. still, this is the best option for your first 10 if you have the income on-paper, but yes, you would be paying on 10 different mortgages one at a time. 

You won't be able to refi and get your money back, so make sure you're satisfied with the COC return.I'm skeptical that it needs $0 repairs.Vacancy and Cap Ex might be a bit on the low side, I don't know your area.

The only downaide I see for duplex is its cap rate, it seems to be a little harder to recoup income faster but probably much less headache.

You can probably learn it on your own and I'm not sure how being an agent would help.I think starting out as an agent with no experience in selling or even owning real estate would be a difficult endeavor. 

They'll go up to 90% LTV but I'm capping out at lower than what that amount will be because the highest DTI they'll do is 50%.  

What a difficult choice. 

Most lenders cap out the amount allowed on a sellers second. for example if the lender is giving you 75% LTV on the purchase they may allow an additional 5% on a sellers second leaving you still stuck with the 20% Have to have some skin in the game

Dealing with difficult situations successfully is something that can add a lot of value to a deal.

. $250,000 for a single) not the cap gain.