Connecting a LR catalog that has been built from Smart Preview's is super simple! 

Just check out the video on instructions how:

Please note we recommend that until your order has been completed and all images checked that you keep a backup of all files in a secure location (different from the one you will actively be using). Meaning the original LR catalog and Smart Previews you built to send in for your order be saved. We show an example of this during the video.

*****Additional note: To speed up the rendering process you can select all images and in Library mode Previews > Render Standard Sized Previews.