For the past 3 years, I've paid my property manager in Costa Rica via paypal, a minimal cost for me and he gets his money next day.   

That HE loan would make you cash flow negative on the first property, especially considering you are not even factoring in any repairs, maintenance, vacancy or management.

Plus, they handle online rent collection (a necessity if you don't have a property manager!)

I have traded maximizing cash flow for ease of management. 

While this isn't a hard and fast rule, more often then not, these are the guys that can't manage their schedules well, and will be gung-ho on your job for a couple weeks, then be flaking out as they picked up too much work and are trying to keep too many homeowners happy.And lastly, the more detail you have the better the bid will be with few change orders.  

I will be self-managing remotely (from NJ).

I would be able to manage the finances, marketing and showings even while working but maybe not attend to the small stuff such as getting a random call to fix something stupid at 3pm when I'm 6 hours out of town or on my 30th day of night shift 12s. 

I think you nailed it already, they probably just have too many deals to manage as flips.

Come to think of it, what happened to the my-property-manager-is-shacking-up-with-my-tenant posts?

On the other hand, you stated that the management firm was charging 15% and had a 15k expense.