The bank statement would only be needed from the first day - the Trial Balance would include this from the previous periods. But yes, just import your trial balance and your clients, and you should be set to go.
The Trial Balance would include all previous invoices - your Crunch records would be the backing source for these, so ensure you can still access this data once you switch, or at least make a back up. Crunch should be able to advise on this further.
The only thing you may need to adjust is outstanding invoices. This would just involve raising an invoice on QuickFile and reducing the balance on your trial balance. This thread may help with this: Opening Balances / Client Invoices
Generally speaking, it should be. But if there are any queries, then the original documents may be needed. The cost depends on the volume of data in your account. When the time comes, you can use our comparison service and find a suitable accountant
Hope this helps!