For real time discussion, yes let's create #bitmark in freenode.
Either a forum on the Bitmark website or perhaps another thread here on bitcointalk might work for the discussion part of it.
We have already proved it possible to have useful discussions on bitcointalk. One thread may not be enough.
We can prefix discussion threads with [BITMARK] and post them under alternative currencies.
This should work for the time being. It is good to keep discussion in a place which is active, if we need our own distinct discussion forum later we can create it then.
Thank you, these are all reasonable suggestions which we can utilize quickly.
Github and Trello for organization.
Bitcointalk and reddit for open discussion.
IRC for real time discussion.
Website, twitter and the usual things for those who wish to keep updated but not necessarily engaged.