Hi Randy,
There are rough guides. Say your file is 1000 x 1000 total pixels and you wanted to print it at 10″x10″, you then have 100 pixels per inch for printing. (1000/10) That is good for lower end production. For nice crisp images to be viewed up close, we like to shoot for 300 to 600 pixels per inch for good quality prints at our shop. So, a 20″x20″ finished file could be 6000 x 6000 total. FYI, we have raster image processing software that can upsize pics to any size if you want to go big. Thanks, Signsmith. PS Those pictures look great.