Can I import historical bank balances?

Yes. The Migrations wizard supports historical balances and reconciled-transaction continuity (M4 and M5 of the migration suite). You upload a CSV or connect Xero or QuickBooks; opening balances post as a journal on the import_cutoff_date, and pre-cutoff bank transactions land as already-reconciled so they don't muddle the reconciliation inbox going forward. Start from Settings → Migrations. After import, your first live reconciliation only sees transactions on or after the cutoff date.