You can certainly add templates by setting up things the way you want them and then clicking "Add". You can also have multiple pictures on one page (e.g. 2 5x7s on an 8.5x11). What you can't do is mix multiple sizes of picture on one page.
Same here, Geoff. I love LR's overall approach to printing, but a built-in "picture package" capability plus the ability to print to a file and convert to a profile are really needed to "complete" it for me.