@Karen O.I believe for commercial its not required by code due to climate zone based on current codes in 2004.  

Apparently one of the neighbors had an issue with the dumpster being where it was for a few weeks and called neighborhood code who then came by and put a stop work order on the duplex only.

There is a GREAT deal of tax topics and situations and the tax code is MASSIVE.

One problem you may run into is the venting of the unit so make sure you check on what the code says on the venting of the units . also they have a Gas as well as electrical for them .

Is PVC up to code for dryer vents in your area?

Today I got a notice from Department of Community Development - Code Enforcement Division, saying that grass and weeds on the property have some violations, like being unsightly, irritation to throat, etc.

I can't answer all your questions but here is a link to 1031 information from the IRS that should help: https://www.irs.gov/uac/Like-Kind-Exchanges-Under-IRC-Code-Section-1031

This list would contain the zip code and corresponding name of the municipality, and a breakdown of the number of SFRs.

What codes do you usually look for?

It will just take research to determine to violation and cost to being up to code.