I don't begrudge people sneaking into our country to build a better life for themselves or their family, but I also don't want to support them or open myself up to risk.

@Jimmy Johnson rentometer is pretty good as long as you know it lumps together duplexes, luxury apartments, SFR's etc. make sure to only compare the comps that are like to the building you have. 

Property currently has a residential building that we run our business out of, is a STR for the events, and sell parking also for the events. 

Most notably is Intel, who is investing $20 billion to build chip manufacturing plants just outside of Columbus, which estimated to create thousands of new jobs.

BiggerPockets has a section just for this, Under the BUILD YOUR TEAM tab- Meetupshttps://www.biggerpockets.com/...Best of luck to you!

My goals with REI is to generate as much cashflow and appreciation as possible, so I can get out of the 9-5 routine, build wealth for my future, and have as much time for myself as possible.Is Southern California a tough market for beginners?

Absentee development is very challenging unless you have a very reliable team.

So rentability is a factor for investment as well has potential to build good equity.

If we purchases a home as an investment property, build a DADU, and sell the home and DADU (around 12 months after the purchase), what's the best strategy for tax saving?

The key is buying properties significantly below market value, keeping costs low through self-management and maintenance skills, and taking a long-term view to build wealth through forced appreciation and equity capture over time.