Questions: Are the accounts rolled over at the end of each financial year or do they re-start from zero each year. Are previous financial years locked, but viewable, or completely open, to view, amend, alter. Can previous periods be locked after accountant/auditors amendments.

There is no rollover required. No accounts are reset to zero. The balance sheet report automatically moves current year earnings to retained earnings based on the date selected. Hence you maintain full history.
You can lock any period by using the closing date feature, you may notice the closing date is displayed in the top right hand corner next to your account name. No transaction can be modified prior to this date. You set this date in Setup Menu -> System Customisation -> Accounting Period. Change the "Current Period" to the date you want to lock up to. Good practise is to move this date each month as you reconcile/publish your accounts.