But if I buy an investment property using a loan, I won’t be able to later use an FHA loan when I'm ready to buy in LA, right?

If I buy a vacation home using a 2nd home loan and rent it as an AirBNB when I am not using it, can I still do a cost segregation study to accelerate depreciation and offset losses against my W2 income if I follow the rules of STR tax loophole (I.e., the average stay in the house is less than 7 days, I manage the AirBnB myself, and spend 100 hours or more a year and more time than any other person/entity on managing my AirBnB business)?

Generally using a loan to make a down payment on another loan is not a good idea.

I’ve been using a properly management software Hemlane for couple years with no major issues.

I'd also like to note, using a Realtor can be a great advantage when it comes to renting your property.

You could rehab a distressed property using a fix-and-flip loan and then refinance the loan into a long-term DSCR once the repairs are finished.

Loopholes are legal and allow income or assets to be moved with the purpose of avoiding taxes.I just want to make sure that people don't get the connotation that using a loophole is illegal, it is not. 

I toured one slum lords building to possibly buy and the tenant took such good care of his unit but there was mold everywhere and the bathroom light (not the light bulb, the light itself) had gone bad I guess 5 - 10 years ago and the tenant was just using a lamp to shower with.

If you're not already using a realtor, I'd be happy to help. 

My house hacking plan is to get a distressed MFH using a FHA 203k loan with about 3.5-5% down, and fix up the property to increase my equity.