Adding a single ADU in southern CA is typically a poor investment.  

Here's an article with things to consider when selecting a cost segregation company.

For the flip itself, this would mean a GC or better yet, have a crew there that can handle 60-70% of all the work meaning they are there working on it the day you close and stay there throughout the process till it's completed. 

If you don't have such a clause, add it.

Just bought a property in cabarrus county and turned out the crawl space doesn’t just need a vapor barrier it needs to be incapsulated, with trenches a sump pump and an industrial dehumidifier.

This is a really good question and one I was asking a year ago when I decided to jump into the MTR business.

I am a similar situation. 

A mix of competitive pricing on airbnb-- it's not the same pricing as a STR---remember that.

@Heidi Fahringer wasted time doing several calls and then a meeting with a CPA and then got shocked with their proposed fee.After even more wasted time trying to find out from them why the fee was 10x what I had been paying - a lightbulb in my head finally lit up and I asked the revealing question and found they had a minimum charge.Obviously, we were not a fit.

Here's an article with things to consider when selecting a cost segregation company.