I am fortunate to have a wide-format Canon printer which prints beautifully on 12" textured cardstock. I don't often print photos at home, but when I do, the Canon prints are nearly identical to those I print at the developer. My wide-format printer is, hands down, my favorite scrapbooking tool.
To print directly on a 12x12 sheet, I first set up a 12x12 blank document in Word. As I'm figuring out my layout design, I determine where on the layout I would like my journaling to be placed. In my Word document, I create a text box for the journaling which will fit in the required space on the layout, then I move it around in the document until it is precisely where I want it to be. (Occasionally I set up blank text boxes to represent the photos on my layout, which makes precise placement even easier.) I save the 12x12 page inserts out of new albums to use as test sheets for my journaling and, once the text box is in place, I print the journaling onto the test sheet. I fit my photos around it, and adjust the position of the text box if necessary before printing on my final cardstock.
Cardstock: Bazzill; letters: QuicKutz Studio; Brads: Making Memories; Circle punch: Paper Shapers