will 3b has a steady market?

You might be able to get a better yield by finding a value-add project or a BRRR type property, but the market rate stabilized is 4-6% probably.Just be careful of insurance right now, it's been going up and seems to have stabilized, but it's still all over the map depending on the specific property and who is doing the insurance.

Similar to you, I'm thinking about other strategies for off-market leads and tried direct mailers, but not sure how effective that is for multifamily.

I don't know what market your rental is in.

Setting up networks of agents, contractors, and wholesalers in various markets. 

@Chris Elliott There are many options left in the market.

Market changes all the time. 

I definitely would be careful if you decide to consider them- he had all the right answers, until it was time to actually move forward.  

In the NJ market how likely is cashflow in the first two years?

Helocs like this technically exist, but can be complicated to actually close.