I also use pricelabs to automate my daily pricing by making weekends more expensive and weekdays less expensive, fluctuate prices with seasonality/demand, and requiring longer nightly stays when guests book further in advance.

The change in your cash flow is also important to consider.I'd ask other lenders what rate you could get assuming a middle FICO of 730 (based off what you said your credit is)  You may be able to get a little lower.Those numbers tend to fluctuate a lot. 

I prefer to leave mortgage as one calc and lump insurance and taxes in with this 40-50%. things that make it fluctuate significantly are age of property, how much work was done up front (to prolong CapEx expenditures), and bedroom size.

Those fluctuate with the 10-Year Treasury primarily.

Pay close attention to when the comparable property sold: The more recent, the better—real estate prices can fluctuate rapidly.

Potentially you could run into trouble if the units are individually metered but the rents aren't fluctuating with monthly utility expenses.

Or is it based on the rent fluctuations locally?  

This affords room for market fluctuations and the fact that taxes would apply should the "reserves" need to be tapped to help pay bills.  

Since we charge different monthly rates for Dec-March than we do the rest of the yr and since our electric bill really fluctuates depending on how our guests use the a/c (seriously, can be $57 or $167!)

This can be a barrier to entry for some investors who do not have the funds available.Market Volatility: Real estate prices can fluctuate based on various factors such as economic conditions, interest rates, and demand.