Just going by what I counted in the list as of right now:
Does not necessarily mean certain slots NEED to be filled - I'd say play whatcha feel like playing. I'll probably be trying to do the surveys to get up to 500 ZEN, which I believe gets you 2x character slots per purchase. This'll let me level up another character or two, and still have space should a new class be released that I may want to play.
Of course, there is the whole issue of bag/bank space...meh.