QuickBooks Online will take a three-column Date, Description, Amount CSV. That is exactly what this produces, so the file does not need reshaping between download and import.
This is the format to use when the statements are older than your bank feed reaches, or from an account that was never connected to one.
If the account is live and connected, a feed is simpler and free — use it. This is for the statements a feed cannot reach: periods before the connection, accounts that are closed, and institutions that will not connect at all.
Importing is the point of no return — bad rows are far more work to unpick than to catch. The reconciliation runs before you download, so you know whether a statement ties out before anything reaches your books.
Batches of up to 25 statements convert together, which is the usual shape of a catch-up engagement.
No — for a live, connectable account a feed is simpler and costs nothing. This exists for statements a feed cannot reach.
Date, Description and Amount, in the three-column shape QuickBooks accepts.