My suggestion: Have one LO printed first and then see if you are happy with the results from the printer/developer you choose. If something is not right than at least you did not pay for 8 bad prints - - just one.
It will also allow you to make any adjustments to your LOs if necessary. I found that when I was having 8x10s printed, anything too close to the edge of the LO is cut or is right at the edge - - it bothers me!
It has something to do with the way the printer is setup. Even my borderless home printer will do this unless I make an adjustment to the printer setting.
If you are doing 12x12 and the company you are using does not offer 12x12, you will of course have to choose a bigger photo paper size and then trim to 12x12 - - if you are doing this than you should not lose any of the LO. You can also have other things printed on that same piece of photo paper so that there is less waste. What I have done is open a new document in my scrapping software that is the size of the photo paper offered by the printer and then I have added other photos as they fit - - a couple of 4x6s usually - - but that would be up to you and again would depend on the photo paper size. Of course, you would need to save the "NEW" document as a JPEG - - the format most commonly used by the industry - - to avoid problems and confusion with the printer.
HTH!
ccc