Is it really a good idea to build content for a support forum prior to its launch? I mean isn't the members who have queries ask the question in support.
Its always a good idea to build content when it comes to forum whether it is a support group or general community board. Build content about the general 'how to's' that you think the members will have queries about in your forum.
Content attracts content when it comes to forum. No matter how popular your site already is still you will need content for people to join in your board.
An interesting content in which will support the forum will provide great discussions as well as benefiting the members.