Starting a yellow letter campaign.  Any Input Advice Appreciated.

I bought a list of homeowners off listsource with the following parameters.  I think Sean Terry said this was close to the best parameters for getting a good response.

City of my choice
Total Assessed Value 0 to $100,000
Property TypeResidential: SFR
Length of Residence10+ Years
(Household) Age65+ Years
ADDRESS-COMPLETENESS Mailing and Property address Complete
CORPORATE-OWNED Exclude

I got 327 from the above criteria for $57.  I plan to mail to 100 at first.  49 cents a stamp.  Total damage about $107.  $107 isn't that much money unless you don't have $107.

I plan to write everything in red pen and I almost failed penmanship growing up - so my writing isn't too good.

Envelope:
My Home Return address - I have some return address stickers laying around I plan to use.
Write their address in red pen.
What color envelope?  Invitation A6?
What stamp should I use?  Spiderman to American flag?

Letter:
I plan on using lined legal paper.

Says:

Dear X,

I would like to $buy$ your house at 123 main street.

Please call me,

Kirk
Google phone number that includes my local area code.