However, as I poke around and talk to folks, it seems like per-unit cash flows can be pretty modest - sometimes only $50/mo or $100/mo per door. 

Really, it's just like any other activity that consumes your time.

HELOCs, when strategized properly, simply give the consumer the flexibility to decrease the amount of interest and time on a loan.

Lenders who originate these loans are generally required to keep them opened for a period of time ranging from 6 months to a year depending on who the investor is on the secondary side of the market (this isn't general consumer knowledge but lenders know this).

It can be a very consuming endeavor and if one of you is not going in whole heartedly it is a relationship disaster waiting to happen.The bottom line is that if you have a good rehab team, then there is enormous profit in repositioning a property.

It's moreso for consumers than investors anyway. 

Moving tenants out will be costly and time consuming.

Really looking forward to the journey ahead.I've got a modest sum of money that I would like to use to get started in real estate investing. 

Shopping around for specialist is going to be difficult, and time consuming (holding cost is going to be higher as well, fyi).

The tsunami of cheap money is simply a way of consuming future productivity here and now and we will have to pay.