CoC is also calculated after you have estimated all your expenses and then subtracted what you will be putting away for capital expenditure - you are estimating this, right?

Interest income is taxed at ordinary rates and you can subtract legitimate investment expenses whether in an entity or not.Your friend could certainly open a separate bank account and track his lending income and expenses separately in any accounting program he might use.

If we build the casita now and then refi, my contractor thinks the appraiser is likely to notice the casita is unpermitted and add $0 or possible subtract from the value. 

The total amount owed, principal, interest at default rate, legal fees, processing fees, filing fees, foreclosure fees, etc. will be totaled and the amount the property sold for subtracted from this number.  

Know that Effective Gross is after debt services before after expenses subtracted.

If this new total is lower than your current monthly expenses, your current home's low-interest rate might be more of a financial constraint than a benefit.Factor in Potential Rental Income: Since you're considering a multifamily property, don’t forget to subtract the potential rental income from your new monthly obligation.

(Just take your old rent and pet deposit, add them together, subtract what you’re allowed to charge for pets and list it that way instead.)IE. old listing was $1,500 plus $100 pet rent    New listing is either…     SFR 3/3 NO PETS!  

Personally, I would keep a running ledger with additions and subtractions.

Depreciation will get included (subtracted) each year (I always date that on December 31.)  

In most markets they are value subtracts (I.e. add less value than they cost).