What are some of the things that get most overlooked when buying a condo that will be good know about to prevent unnecessary issues from coming up? 

If I were in that situation, I would definitely not do any unnecessary work. 

Finding a broker and working as an independent agent:a) Just about all brokers will qualify you as an Independent Contractor (IRS exemption to the rule), so there is almost nothing mandatory that they can impose on you.

There are definitely a few benefits to keeping them separate, and potentially legal implications depending on where you invest:Opening a separate account for security deposits will ensure that there's no chance of them being spent - this is the one that might be legally required as well.Keeping a separate "operating account", even if you're not a business, can absolutely help you keep the two sides of your finances apart and more accurately track income vs. expenses and the reserve level that you have for the properties.Theoretically, if you're using a very detailed budgeting/outflow tracking application or scheme, you could make the operating account unnecessary...but it's a very small action that will help you simplify things greatly, especially around tax time.

The water company said the water softener was unnecessary, as they have a new water treatment system.We got tired of traveling back and forth to the property to work on it, so we pitched a tent on the porch!  

Another downside of HOA's are the restrictions they impose on tenants and business vehicles.  

Typically, HML will charge around $1500-$3000 in fees, most all are unnecessary.

The second most important thing is to make sure the lenders don't experience unnecessary delays with closings.

For 3+ families it'd also be good to make sure they have a current green card (issued by the state of New Jersey sort of like a certificate of occupancy renewed every 5 years indicating that the building passes whatever requirements the state imposes). 3 story buildings with 3 units need to have a fire escape, exit signs, self-closing doors, etc.

They are all just unnecessary drains on profit.