I was wondering if anyone had any strong recommendation or contacts.

As @Joe Splitrock and others have mentioned, the simple answer is to go back to work in the same field you were working in, hopefully quickly and in a higher paid position, and continue building a strong employment history in your area of expertise. 

There is strong housing demand in all of the 9 county area but "30 minutes from Knoxville" includes both areas of exceptionally high and limited, price sensitive demand.  

I’ve got strong equity positions with a few different rentals and would like to have access to additional cash, but every lender I’ve spoken with so far can only do HELOC’s for primary residences.

And re: changes in the market, what if the market is continuing to appreciate strongly?

I strongly suggest you get a new PM.

Tenant screening and strong screening criteria are very important, NJ is a tough state to pick and choose your tenants so you need to be very clear as to what you require and it also has to fit the section you’re trying to rent in.

My strong advice is to start attending some local real estate clubs to begin building these relationships and developing your resources.

Brokers appreciate and value the feedback and it also allows you to build a strong relationship with them.  

Russell's right on: Virginia within an hour of DC has been a strong market for quite a while, and Amazon's HQ2 announcement at the end of 2018 just turned the heat up even higher.There are buy and hold opportunities for sure, not limited to SFH at all.