It is all depending on the City rules and regulations.

Investments in a QOF The proposed regulations clarify that, to qualify under section 1400Z-2(a)(1)(A), (that is, to be an eligible interest in a QOF), an investment in the QOF must be an equity interest in the QOF, including preferred stock or a partnership interest with special allocations.

Classic case.Your first responsibility as a landlord is to learn all your state landlord tenant regulations.

Although I feel the residential single family homes are a bit more 'protected' now than they were in 2008 due to more Fannie Mae backed loans and lender regulations, I get the feeling that commercial complexes (multi unit apartments in particular) have been built at an astounding rate for the past 7 years.

On a main road I would convert to an office environment, or rooming house if the area supports it.

There are parts of this arrangement that we cannot control, such as how the HOA is operated, how the fees are increased, and in some buildings the HOA regulates the percentage of rentals to owner-occupied units are in the building. 

What's the best plan to ensure I can protect my rental house, and provide a safe environment for the tenant, without costing me too much money.Finally, who is responsible for paying for the repairs?  

@Ryan Gillette is generally correct however it's not so black and white, especially with the new IRS tangible property regulations.

On the northern east coast I’m not sure we’d have enough sunlight to warrant such a cost and our winters are pretty brutal so we often use trainloads of heating fuel  Can’t put a price on saving the environment 

Many states have vastly different regulations on what is and what is not acceptable.