Honestly... I'd engage the services of one of our implementation consultants.
They've done it several times before and their experience and knowledge built up over the years means they can do it efficiently and will follow best practise plus be prepared for common "gotchas" that arise as part of the data migration. This is their bread and butter.
I won't stop anyone from having a go, but like anything: you may end up investing a great deal of time and effort getting skilled up to do a good job only once, or will create issues because you're a novice to the task and won't know where to look. If you're interested simply in outcomes of value in a short time, reaching out to our specialists is a safer approach.
