I tackle all my deals based on 70% ARV, then subtract repair cost (pad it out a little) to come up with a target price. 

Accounting for known reno costs (water+mold) subtracted from $133,000 I get a purchase price of $61,500.

Would I be able to write off everything I spent on the flip and subtract that from the profit so I pay less in capital gains? 

Next, subtract the balance of your mortgage.

Subtract out all the expenses (not the mortgage).  3.  

He subtracted this area from the living space square footage.

I think the Cap Ex in this formula is just saying to subtract any capital improvement expenses. 

Subtract the costs to build, and you're right there. 

The STR is a job as much as it is an investment, so you have to subtract your time from that cash flow.

If the current owner doesn't have leases, in my experience, run for the hills.Expenses:Next you want to figure out what you could net from those rents by figuring out your expenses:-Insurance-Utilities (if the tenants don't pay their own)    - electric    - water/sewer    - heat -Taxes-I'd factor in a percentage of the gross rents for maintenance depending on the condition of the property:   -when the roof was last done   -water heater   -boiler   -when the property was built-Management (if you aren't going to do this yourself)Debt Payment:After determining your Gross Rent and subtracting your expenses you will have your Net Operating Income or NOI, but if you hold a mortgage there is one more expense you will need to subtract, your payment.NOI - Mortgage Payment = Annual Cash FlowDivide that number by twelve to get your monthly cash flow.I hope this helps.