@Joshua Redmond a good ol phrase to remember is "if the seller creates price then you create the terms" all of your questions are all factors of negotiate to get best deal possible for either party.

How do you recommend I phrase this in good terms in the addendum to the lease?

If you want to learn more about a specific city, you can also set up key word alerts, so you will get a notification each time that word or phrase is posted. 

My favorite phrase applies here - everything in real estate is negotiable.

I phrased the question poorly - do you see a difference between buying one unit of a 2 flat vs. buying a condo in a larger building with lots of units?

The phrase "then current underwriting requirements" refers to qualification, not loan terms. 

When you try to market the property to your buyers, just be careful how you phrase things.

When starting out and doing most of the work yourself (or paying help in pizza and beer), remember perhaps the one most important phrase in this wonderful rental business:  "THE ONLY THING WORSE THAN A VACANT UNIT, IS A UNIT WITH A BAD TENANT IN IT."

The phrasing of the question makes me assume you have not yet researched this enough to buy a property yet. 

But I think you're misunderstanding what that means.The way you phrased it isn't clear.