Or if you charged the same price, but had fewer turns. 

We also have a rental property out of state we bought with a conventional loan about 5 years ago and we didn’t put 20% down on that.

But conventional will require 15% down just because of property type: duplex. 

If the norm for a duplex in the area is that the tenant does lawn care I would stick with that model, you could add an addendum to your lease that says XX dollars is charged if there are any citations against the property.  

The only problem was, that renewing cost was double and depending on your plan, they also charged me $100 for every service call.

Yep, no conventional loans, pick your poison.

It’ll be a $450K conventional 30 year with a loan to-value-ratio of 65%.My credit scores are 717, 715, and 705.

Do we charge a little less if she signs a 18 month or 2 year lease?

What Ido is charge a fee equal to the value of one months rent. 

Some of my prospective sellers who might agree to a lease option with me can't sell their house conventionally because it is probably overpriced.