Figuring the figures to see if a possible cash flow can be

To do figures to determine whether or not there is a possible cash flow is to do this:

Find out what the mortgage payment would be on listing price.
Subtract expenses such as insurance, taxes, any utilities that may be needed to show the house, (winter, lights, heat), summer (water for lawn), advertising fee $500.00 perhaps, replacement expense and anything else.

I’m thinking if the house had to be rented because it was not selling “just yet” holding costs, and other costs as well need deducted, too? Then you can see what is left over, right? There may a few more things in here to deduct as well. Or do I have this all wrong? Can you help me a little bit with this, please. Oh, I too appreciate all of you and this site!! I also enjoy the people asking questions!!