Couple basic calib questions

So finally I have had my main monitor calibrated.

Couple of questions:
1) When I open a file I get a prompt:
The embedded profile doesn't match that of the working space.
I can either:

• Use embedded profile instead of the working space
  
• Convert the profile to the working space
  
• Dont' color manage

You can change that in prefs, I think. Maybe someone remembers?

Costco wants sRGB jpegs. They probably use a Noritsu 3101 printer. The ICC profiles for your store can be downloaded from Drycreekphoto.com.
I forgot the profilr once & didn't see any difference in the print, but my store had auto corrections turned off. They said that the differences are so small that they don't see them, either.
When you save the profiled file, UNcheck the "Save profile" box.

I like the lustre prints.

They're so cheap that I usually "proof" a 12X18" print?
At times I've made a few 4X6" prints of a 100% crop just to check the colors at the available resolution before printing a 12"X18" print. The colors of the small print have been consistent with the final large print.

Answer to number 1:

Go to Edit > Color Settings.
Under Color Management Policies are 3 check-boxes. You can either uncheck them (not recommended) or change your working space to the one you plan to use (recommended).

Also you can check the Color Management Sticky for more info.