First, congratulations for going above and beyond what most agents will do for their clients. I would emphasize in any contact that you are working with a specific client who has targeted an area and that this is not a generic contact for any and all listings.
Almost anything you do in this process will set you apart. I would discuss your clients desire for the neighborhood, but not mention the reason for their preference, as it is a fair housing issue that could come back to bite you.
Identify all the potential 1 story or 1 story with basement homes. Create a list and make notes as you go, you'll need these later. Have a general idea of value, but avoid mentioning a specific price until you are able to view the home and assess it's size, age, condition and the comparables. Tell the story about the neighboring home they missed out on and how this is your motivation for knocking.
I would create door hangers to leave at homes that you don't make contact with that you can still leave with your contact information and a description of what you're looking for when you are able to meet someone.
1%-2% is a good return on mailers, so chances are you won't have much success doing that alone. A campaign of mailers, door hangers and knocking will give you the best chance of finding a home for your buyer and making one heck of an impact on an area. You'll likely have returns on this effort for years to come if you do it right.
Best of luck, just do it as soon as possible.