Hi @xtian,
Thanks for reaching out!
As far as page set up, the canvas is where you'll build all of your web apps. We don't have a way to configure the canvas to be a specific page size. You can control the width of the cavas - as described in our docs, but the height will be automatic. Components will then be configured to fit within the canvas based on our 12 column grid. The canvas is specifically for creating web pages that can be viewed on mobile or desktop.
We do have a couple of ways to generate pdfs with information from your web apps, which it sounds like could be helpful for your use case. Unfortunately, we don't have any settings for controlling the page size or orientation of the generated pdf. If you use our utils.downloadPage functionality, it'll download the page at whatever dimensions the viewport is in. There is no way to specify a dimension for the download.
We don't have a direct print functionality in Retool, but you can download items from Retool (as pdf, excel, etc) and then open those items on your computer to print them (as described here). I'll add your +1 to the internal feature request where we're tracking use cases for printing from Retool. There's also a helpful discussion about printing here