It's just another operational expense added to all the others to determine the value.

In both cases the bank will appraise the building (i.e. multifamily, commercial or otherwise) because the value of the building is required to determine how much the bank is willing to lend.

Your regular income gets added to the cap gain for the total that determines what bracket (0, 15 or 20%) you fall into. 

Is there a way to determine whether a real individual is bidding against you or that it is auction.com algorithm seeking to boost the price?

Not every agent understands investment real estate and they can lead you far astray.Know your numbers and dive into the forums and info on BP.Meet with a RE attorney to determine structure and get advice on the best place to start with your financial capability.Get a GREAT CPA to ensure your tax liabilities are minimized to the greatest degree.Find an INVESTMENT banker in your area and establish a solid relationship so when you find a deal they are willing to help you out.

You can also do research online to determine population and job growth, it's a good sign if large companies are moving there.

There are different ways to do that which you can research and determine what feels best for you.

Austin is a great market for investing and depending on how much you are wanting to invest will really determine what area best suits you.  

I am trying to determine our real cost of having one extra person live in our household.  

Whether or not it's capital gain vs ordinary income subject to SE tax is the million dollar question.Not enough information was given here to make that determination, which is based upon fact and circumstance.