Reach out to your accountant or Xero Support.
Right now, you can only select one deposit account. It's not currently possible to sync to a different Xero account based on payment type or gateway.
No. All we can do is dictate which account to post the item to (income/assets accounts in Xero -> Settings). Otherwise, reach out to Xero support directly.
Xero is invoicing, QuickBooks Online is sales receipts.
You would need to work with Xero Support to extend any trials you are currently receiving.