Performing adequate due diligence is paramount in commercial REI in order to determine true expenses (or accurate estimates) and to be able to adjust the asking price for deferred maintenance issues, etc. 

Your job likely is going to command a good deal of your time so the quality of your team will be paramount.

FPS is extremely expensive and can turn a great investment into a costly liability.Understanding proper zoning and land-use prior to purchasing a multi-family property is paramount to a successful investment.  

Other than having your funding lined up and a mentor on board, buying great deals is paramount.

Purchasing a STR in the Tahoe area in the early 2000s... location was always paramount, however, some of the STR market also has to do with the culture and trends of the time. 

And the company you hang your license is paramount to how you run your investor business.

IMHO - the "vacancy rate" is a moot point, since it is what you want to make it.If the rent is under market value - then the rate is very low.If the rent is too high - then the rate is high...As mentioned above, boots on the ground is paramount.  

Dawn's point 4 is paramount.

Properly vetting applicants/tenants is PARAMOUNT!

Requiring the contractor to carry coverage AND ensuring they do by affirming it with the provider (info found on the Certificate of Insurance - COI) is paramount to every investor.