cubecart website move and upgrade

I want to move a cubecart website [login to view URL] from [login to view URL] to godaddy.com. I presume it would also be best to move the domain name in order to keep seo rankings etc? I already have a hosting package with godaddy. I also want to upgrade the cubecart from v4 to v5 and I will purchase the licence key when ready. I would also like a mod installed which is an Amazon checkout mod. I believe this requires an ssl certificate and I have this purchased and waiting on godaddy. I know a company called Havenscroft do an amazon checkout mod and I think this might be the thing to use unless of course you know of something better. I don't know if it is best to move the website first and then do the necessary upgrades or to do the upgrades first and then move but I would accept what you say in this matter. I also have another website at oneandone which I would also like to move.