Great, really fun concept.

Two very interesting things I looked at yesterday, little bit related to this, was two different projects from a german artist, that was to promote going out in the street with your laptop and do part of your work outside.
One is a portable wifi-router, that creates free internet surfing in a public place, and placed so that you are going to have to be outside (the range it covers is not going through walls) and movable between different places depending on what weekday it is.

http://datenform.de/openinternet.html

The other is secretely placed USB-memory-sticks hidden in the cracks of a brick wall or similar "semi-public" place, to create a spontaneous peer-to-peer-file-sharing-system locally. Totally fun concept, and off-line from internet, but with potentially a good reach for people in your area:

www.deaddrops.com

You should try to think about how these could be modified and added to your lovely concept.
And you could also think about inviting some architects to sit at your café tables, to give away advice to home-builders, help them with some construction blue-prints, sketches, dimensions of materials/walls/insulation, advice on building permits...
Perhaps a professional from the stores suppliers, to give advice on material and tools. Have demos of new equipment...
Perhaps get an expert on homes energy costs / electricity efficiency to help customers reduce costs and carbon footprints...

And by the way, there is a little trend coming now with "home-brew" traditional coffee as a backlash against the overpriced mocca-frapp's... so as you said, forget about that espresso-machine.

Perhaps you should add a link to the inspirations regarding spontaneuos discussions/meetings :

http://www.openideo.com/open/vibrant-cities/concepting/dialog-booster-park.

Mike, this is such a great idea and I love the photo you chose! I especially like that you've left it up to the business owner to determine the best way for his or her business to interact with the greater community – and that it doesn't have to be an expensive commitment! Great work.

This one really resonates with me, perhaps for its wonderful simplicity.

It can be as simple as installing a bench outside a restaurant or store, but that bench can catalyze all sorts of lingering, conversing, and even business transactions, attracting others on the street to join in the interaction.

The DOT's Public Spaces Unit might be a helpful point of reference.