I would get a medium-high end dedicated with whatever control panel you are currently using - to ensure smooth transfer.
Management of the server is probably your biggest issue.
Befriend an experienced server admin. Perhaps you can pay him to setup/configure your server and security harden it. (Do NOT ignore security issues, something a lot of newbies neglect - you will pay later) Keep buying him doughnuts, for maintenance that would be required at a later date.
Most servers come with 1000GB bandwidth. I would say avoid unmetered servers.