exporting a print-ready poster file from adobe express?

I think I have the paid version, (with my Photoshop subscription maybe? - there's no prompt for me to upgrade and it says 'Premiere member' in the top tool bar), and there is the option to resize the image, but no option to change the dpi, and no indication of what the current dpi is that I can find. I started with a template for a 5 x 7 wedding invitation intended for print. I tried downloading and printing the file - I wanted to check the text size for readability, but it printed much larger than 5 x 7, so took it into Photoshop, where I found the dpi to be 72. I changed it, and printed it off at the correct size. So it's not an unsolvable problem, but it just seems strange not to be able to change the dpi in Adobe Express - unless I'm missing something. 

You'll want to set the project dimensions to be whatever is needed (# of inches x 300) for both the height and width. It renders at whatever the project dimensions are. When printing you can specify the dpi to print at.

Adobe Express doesn't support saving in a format with color separations. You might need to check with the printer for whether the output options would work. The file formats that it saves in are PNG, JPG, and PDF.