One thing that some people don't consider when designing for sheet-fed press is the gripper margin. The gripper has to hold the paper as it's being pulled through the press, and so it can't place image in that area. I've seen designs that didn't take that into consideration, and unless the layout was reworked or shrunk to fit the imageable area of the sheet, it would push the trailing edge off the page. That could mean either difficulty in trimming/bindery, or failure of the piece as a whole.
So, I'd talk to the printer and find out what the maximum imageable area for that particular sheet size when run through the press they will be using is, and work backwards from there, adding in crops and bleed. What's left will be the maximum trim size of your finished piece. You can always go down from there, but going up might be the factor that kills the project, or pushes it up to the next price point.