Update -
I've successfully install v10 on a new Del box using a USB stick and that went easily.
I backed up my live production server via the console to a USB drive (Putty in as admin - not server manager). The machine said that the backup would be around 55Gb and it backed up in about 3 hours.
On installing V10, I restored from the USB drive when prompted, but it only found a 33Gb backup file. That seems to restore OK and now I've clicked the correct date sort, I think all the email is there ok.
I've yet to try and access the ibays
I've connected the new server to the network now with email collection disabled so I'll see if I can get roundcube and the rest installed.
I think, so far, so good....