Once you establish a proof of concept, I would suggest trying a site like kickstarter to see if you can generate enough demand/presales to help speed the project along (for example, if kickstarter results in a lot of funds you may be able to hire contract developers to speed the product to market). I would also recommend featuring the kickstarter project on your front page and/or creating a signup email list for announcements a la the Raspberry Pi project style to inform people/gather a list of potential purchasers.

I will note that I personally am a tablet PC user. However, I would be interested in an android phone version of the application as a "doodle pad" (I am a Samsung Galaxy 3 user, as the Samsung Note was only available on AT&T and the poor pen integration kept me away from the HTC Flyer).