You will need to upload all your data on our servers and then restore all your databases one by one from plesk control panel. plesk allows you to check your
website hosting with a temporary URL before you change your nameservers so you should verify working of all your
website hostings using temporary URL.
Once you find everything work as per your expectations then you can proceed with nameserver changes. You will get 2 pairs of nameservers and you can choose either our nameservers from those or you can register your private nameservers and point all your domains to your private nameservers.