As for your original question, don’t select “relative”, it adds your given size to the existing size.
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More importantly, doing a brochure layout in Photoshop is not something I would recommend, InDesign is the tool for that. I’d go directly to InDesign for anything that has more text than a couple of large headlines.
But if you’re going to do it this way, just about the only sensible output format is PDF. The main being is that Photoshop is raster (bitmap) based including text, so setting type to print out properly from Photoshop is a real hassle. You’d need to have the file in CMYK format and text in 100 black only (0C, 0M, 0Y, 100K) for black text, then export to PDF to retain text in vector format (embedded fonts in PDF). Doing anything else, you’re going to wind up with the double nightmare of rasterized text that is printed in all four colors.
If you’re overprinting text onto an image, it gets even more challenging…