A great tutorial!
I had two issues, that others might also run into:
* you might have to execute the querys from step 2 manually (as i followed all the steps here to create the product, and didn't acually "install" it via the import product button)
* If you want to create a plugin that changes the template (instead of manually inserting the code into the template modifyoptionslike in step 4) you have to do some extra things - explained in
this thread