Couple of Costco Poster print questions

Hi,

1. If I intend to buy a ready made frame from Michaels, Aaron Brothers and the like,

am I better off getting a Costco 20x30 print made with or without the poster board mounting? In other words, do the off the shelf frames acomodate the thickness of the board, and does the mounting make it look any better?

2. Instead of fiddling with color profiles, if I get a reasonable color print on a 4x6 print from my Epson Photo R300 should I be reasonably satisfied the Costco print in 20x30 will be close in color? If no, is there a fairly easy way to adjust. I do not have a monitor calibration system.

Thanks,
--
Steve