Seeing a $100-300 increase on a single unit is common in NJ.  

Try to buy after 1950 and avoid single family conversions.

You asked about buying older properties and the biggest issues I have found is that roofs need to be replaced, HVAC needs servicing/replaced, and sometimes there are foundational issues (not super common). 

Quote from @Matt Huber: Quote from @Adam Michael Andrews: Quote from @Matt Huber: In 2021 I purchased a couple of single-family rentals.

Purchase price: $500,000 Cash invested: $100,000 Buy and hold multi-family property initially house-hacked prior to purchasing the single family in the burbs.

Quote from @Nicholas Cavato: Looking for advice from you BP pros out there.I will be purchasing either a single family residence or multi family residence home in the Cleveland, Ohio area no later than January 2025 and intended on purchasing using an FHA loan with an already formed Ohio LLC.

Own few condos and single family now looking to expand into multi family 

Super excited to start my new career and new company!

Just be sure the calculate in the interest you are paying on that HELOC into the new project.As for banks, my experience has been that many banks do not like to do HELOCs on rentals unless you have a decent portfolio which they then look at as a business instead of a single rental property.

@Elton Tate is this a single unit or duplex?