Maybe it will spur additional input.

If you don't have atleast an additional $10K saved up you may end up in a tight spot financially if you have an unexpected repair. 

In addition, we can lock a rate while they are still low for a very long time.My question: HELOC or mortgage?

Per my contract I stated that the owner needed to establish a 6 month lease with the first floor tenant in addition to raising the rent and collecting a security deposit.

I had a rental appraisal done for it for additional cost during the process and the results were good enough so that 70% of that number covered my Principal, interest and insurance and property tax payments with a little left over. 

Additional info that may be relevant RE financing.

Additionally, because no-see-ums are so small and are weak fliers, ceiling and window fans can be used at high speeds to keep no-see-ums out of small areas.

In addition to walking the property with a contractor, you could try to partner up on the deal with another investor who has experience with flips/BRRR.

FYI I just confirmation back from Eliot Bencuya at Streitwise that they do only have 1 property now "and that concentration is a risk, we are currently actively pursuing additional properties and do intend on acquiring, over time, a diversified portfolio of quality office properties". 

In addition, in A and B class areas in major metros, the renters are also extremely qualified as the houses are worth much, much more than the apartments.