And I would assume a worst-case interest assumption.

Nice to see actual rents beat assumptions. 

The one that I use all the time is Internal Rate of Return (IRR).What I do is project out the next 10 years of the Investment and determine an IRR based on certain assumptions.

You had to put together the Advanced Business Model which takes your P&L and projects it out to 10 years, make certain assumption on Appreciations using Historic Data, calculate the 10 year Mortgage Balance, 10 year NOI and Cashflows, and boil it down to an Internal Rate of Return (IRR). 

If these properties you will be getting from your parents have been in the family for a long time, my assumption would be they are all paid off. 

Talking over the deal with someone experienced, like a veteran member of the local REIA, is a good way to know if your assumptions are realistic. 

Using some dismally low assumptions...$150/night, 25% occupany, and a 50% expense ratio would allow me to break even while paying them like $500/month (obviously very low).

But again, as interest rates rise, that 5% APR assumption becomes an obsolete analysis metric quickly...TL;DR - Should I even include CoC return % based on actuals in my list of criteria that I send brokers? 

The standard assumptions are a higher exit cap, .1 for each year.If you just want some generic figures.

Brad Hayden made a good list of the initial items you want to tackle -- the goal here is while there may be some sunk cost, you want to find out if your assumptions will pencil out.