I'd like to create illustrations for a book I'm writing in Photoshop. But I'm not sure how large I should make my document, as I don't the graphics to appear pixelated if I end up using them on posters later on. Any suggestions welcome. Thanks
Hello and welcome. Sorry, I missed this thread somehow!
My suggestion is that you make the document (and illustration) as large as your system will tolerate. Let me explain. Not everyone's computer is the same. All will experience some system lag at certain document sizes whereby some of Photoshop's tools will begin to lag, the Brush Tool being the most common culprit. For my system it's about a 5000px x 5000px document.
Photoshop is a rastor based program. Large is best as it scales down easily. Scaling up works well but you could do much better with a vector based graphics program.