I have a series of accounts set up as Metric accounts that are displayed as percentages. For the quarter and FY totals, I would like for these to take the average and not the sum. Is this possible with a Metric account, or do I have to make these Custom accounts in order to take the average?
You would need to make the accounts Custom accounts in order to be able to specify an average rollup for the timespan.
If your formulas contain division, you may want to check the results of the parent levels within your organizational structure to make sure that the results are correct using the Custom account.
Custom and Metric accounts evaluate division at parent, rollup level in the organizational structure differently, so you will want to make sure changing the type of the account does not impact the results of the formula.