A: At present, Gnucash does not offer a way to move groups of splits from one account to another. You will need to move them one at a time. Open the register for account A and select the pulldown menu item View -> Style -> Transaction Journal to expose all the splits. For every split where the "Account" field shows account A reset it to account B. To do this quickly and safely, first use CTRL-c to copy the destination account name ("account B ") to the clipboard. Then highlight each reference to account A by double clicking on it and use CTRL-v to paste the destination account name. Pressing Enter after each paste silently moves the transaction out of the register.
Be careful! If you inadvertently set the "Account" field to an unintended location, you will need to search through all your accounts to find the lost transaction to correct your mistake.
A: This is available from the menu: File -> Export -> Accounts
A: Enter a search criteria of matches regex, and place a single dot "." in the text field area. Then, click Find. The regular expression "." means to match anything.
A: You record the transaction on the date you write the check or initiate the transaction. When it "clears" the bank, you can click in the "Reconciled" field to "clear" the transaction (change the "n"on-reconciled to "c"leared).