Are there 8 or 9 masks in the MQ? I have seven and the game shows 8 on the throne. Is the wooden mask one of the 8 and accessed with the 7? Or is it a bonus mask that isn't shown? Thanks for any info.

The wooden mask is a bonus mask which you have to wear to get the ninth mask. There are 8 you have to get first though to get the ninth.

If you're looking to unlock Konahrik, then yes the Wooden Mask is required.