You only need the account to garage, you don't have to put anything there.

Garage is a place for the collaborating on open source projects and such, where you can use repositories and publish stuff for testing. The account is also used for uploading to extras.

As I see it, you currently have two options. since you have a built in payment function you can either upload the deb to extras non-free (this would require you to set up the packaging to satisfy the extras repository's demands) or upload to OVI store as a free app, but with notes about payment in the description.

Here is the wiki for uploading to extras:
http://wiki.maemo.org/Uploading_to_E...ee.22_packages
Unfortunately we have so few (none? okm there is a couple. Fring for example) non-free apps that the instructions for that are weak.

For questions about uploading to ovi, you have to ask nokia. I believe http://www.forum.nokia.com/ is the place to go.