Hi,
Yes, you can create invoices without sending them.
After creating the invoice click on Save and Send at the bottom. At the top of the next page you can mark it as sent (without sending it).
Also yes, you can do your bookkeeping outside quickfile (for example spreadsheet) and use quickfile only for your vat returns. Quickfille has a bridging module to achieve this:
Note: The bridging module costs £45 +vat (part of the power user subscription)
To keep things simple it is may worth to look into using quickfille for your invoices and bookkeeping as well.
Hope this helps