I'm thinking I should take the deductible for the flood insurance and multiply it by the annual probability of flooding to get an expected annual cost due to flood damage.

This is really a multiplier, you can do as many as you want for your Magnitude and you have a stable market. 

Another good comparison tool is the Gross Rent Multiplier, GRM. 

We are trained, and use the Gross Rent Multiplier (GRM) when looking at our deals, which is essentially the inverse, or cousin of the 1% calculation.

Time is your greatest resource and your best strength when it comes to multiplying money.

Take that number of needed properties, and multiply by the amount of time you think it will take you to find, fund, buy, rehab (if needed), and fill each of those properties with a tenant.

Once you know this, you can get a rough idea what any similar home in an area will sell for by multiplying the median price per square foot sold times the square feet of the house you’re interested in.

From there, I can either take the HELOC or the cash from the refinance (theres about 100K in equity opportunity) and multiply the initial money I had for a down payment to build up from there. 

Find your marginal tax rate and multiply your gain. 

Gross rent multiplier of 142.