Accounting packages such as QBO and others specific to property management are good, but they can also be like killing a housefly with a sledgehammer.

We have insurance for our properties held in our LLC through Westfield Insurance Company and it's a commercial package.

This hands-on approach enables me to obtain useful information, allowing me to make informed judgments and alter my investment strategy as needed.Analyzing these precise elements of a property gives me vital information about its potential.

we build affordable units by doing higher density and I can sell or deliver a housing unit at a lower cost by sharing common elements like slabs, hallways, centrally designed systems, etc 

Your post is confusing because an HOA cannot make a modification to a common element and then charge 1 owner for that *UNLESS* that owner or their tenants damaged the property to begin with.

Most apartment owners will use a holistic management software package and not one that just does accounting. 

Here's the summary I got from the video - she borrowed from bank for mortgage and rehab:Her first property $55k, fixed up and appraised to $90k ($1300 cash flow)She added 6 more properties to her portfolio in year1 - 2 duplexes ($2k cash flow) + 4-bed house (bought from cash flow and equity from other properties).By year1, she made 6-7k profit / per yearBy year2, she purchased package deals and added more properties with 2-week turnaround on fixing them (with the help of a dedicated contractor(s) who lived in one of the multi unit/room properties)She also did Airbnb and arbitrage.

There are a number of guidelines the IRS has for performing a proper cost segregation study (which will pass in the event of an audit) Here is the link to that list on the IRS website:Cost Segregation Audit Technique Guide - Chapter 4 - Principal Elements of a Quality Cost Segregation Study and ReportI have never seen a DIY before, but I'm sure people do it.Depending on the size and type of your property the fee for engaging a qualified engineer-based firm to conduct the study can be as low as $3,000 (lower in certain cases), and the significant benefit created well outweighs the minimal costs.

Are they considered Common Elements and/or Limited Common elements. 

I would first get a quote from your current home/car insurance and see what they would charge you on a bundle package.