I'd say 10% at least, but talk to a local property manager about what's realistic, given the turnover in your area.Find out whether your local county has an online Property Tax portal, and whether you can plug in the property's address to get historical tax data to use for your assumptions. 

.----- Here is my assumptions:1.

My assumption is this is not an option.

If they are then they may give you some basic conditions that need to be done before the lots could be sold separatly.You do have an incorrect assumption though, the conventional loan shouldn't present a problem.

You also need to look at the comps as well to validate your assumptions.

What is the basis for your rent assumption?

Is my assumption correct? 

Should they even be a consideration (with the assumption that they're affordable for me)?

It's not likely you'll have problems with all your properties at once but don't make the foolish assumption that not more than one property at a time will have major problems.

I needed to pull comps & see how much $ we had readily available while making some assumptions on the condition of the property.