How your printing looks is controlled by the themes, and the font size is control by how large your text is on the screen; and that can be changed by zooming in and out. I don’t think @jessegrosjean has mentioned what is the less code that changes the margins when one prints. I think it would be good to get that figured out 
I agree with you that printing is definitively not one of TaskPaper’s strengths, although many power users have found a way to get what they want with way more control over every step of the printing process.
Probably the easiest way to get better printing abilities is using the printing script by complexpoint. You can also try the ruby library to export TaskPaper documents into HTML/Markdown.
In my case I convert my file into a MultiMarkdown file than is then processed into a latex->pdf. All of this is done automatically and through a script that even starts the printing process and archives the file in a filing system. It took me about 1/2hr to produce the template from something I had previously done. If you would like something like that, I can share my scripts. If you are not familiar with Tex, MultiMarkdown and Ruby, this is probably not your best option. But this definitively provides you with the most control on your document’s format.
Hope this helps.