Right. The partner program is a tool for developers to work with Shopify and develop stores for their clients before they hand them off. That, or as a playground for them to try new things and just learn the platform. There's learning resources as well. I would personally work on the unpublished site and swap products when I was ready, unless you have a massive inventory of products because that could take a while and I don't know how keen you are on having downtime. I can't really speak to transferring of domains and naming issues as I've never had to hand off a store to a client before. I usually just do theme edits here and there, I wouldn't want to give you any wrong information.