Note that in listsource you'll find two variations and the details are further complicated based on which one you select:For the "Original Loan To Value" criteria, it is just as you suggest - simple math, at least for purchase money loans. 

Search google for "Hedge Fund Pitch Book" or some variation of that.

You likely may have two options a zoning variation or a Special Use if applicable.  

There's a huge variation of services for such homes.

The deposit is restricted to 2x the rent.[ yeah, this is a Seattle topic, but thought other variations might be useful to be aware of]

In your case, consider dividing the 6,000 into three groups and running three concurrent campaigns with three variations on test messaging (and elements like use of photos vs. just graphics, etc.).

The depth does vary somewhat, though the biggest variation deals with the "rough in depth".

I am using a variation of this but not handwriting (using a handwriting font) - I'm also a developer by day so with a csv (or any kind of spreadsheet) I am pulling the name from the 'Name' column, if there's a first/last name I strip the last name and lead off with a 'Dear James' or whatever.

This is NOT typical however it is not out of the range of normal variation.

Last question - I would think there would be variation in the number of cards sent for each area.