The Wood Stack and Fish Basin are inextricably linked. You need as much wood as you can hold to upgrade your fish and vice-versa. You'll also have to have max vikings for your Meade Hall level and you always need to upgrade your stack before upgrading your Academy.
As at version 1.3, total wood capacity at level 16 is 30,000,000
|Level||Wood Storage Capacity||Upgrade to Next Level|