I have gotten HELOC for home improvement.  

Should I go for a bridge loan to build the Adu now and refinance the newly improved property 2 eighteen months from now?

And it's good to see you're still asking advice on your 13th, still trying to learn and improve.  

I went to school at Rutgers - Camden and have seen the area improve a lot.

The property is a 10.9% cap but there is room for improving expenses.

I would say the best path to improve your net worth  is be a deal finder.   

We did all the managing and repairs, improvements.

Although, the standard of renovation all across the board has improved substantially in the last few years across all surviving turnkey companies I think.

The best opportunity you will have to replacing out-dated systems (plumbing, electrical, HVAC) and improve the energy efficiency of the building envelope (air sealing, insulation, fenestration) is before a building is placed into service.  

These returns can improve if you have the capital to do some value add repairs as well.