Should I reorganize the main service panel when adding a subpanel?
It's nearly impossible for anybody to tell you if you can safely add a second subpanel, based on the information you've provided.  It's going to depend on the service capacity, and how loaded the service already is. 

Your best bet would be to contact a local licensed Electrician, and have them do an estimate on adding the new subpanel.  They will come take a look, and should tell you what would be involved in adding the panel.  This will give you a better understanding of what your options are, and an idea of how much it would cost to simply have a professional handle the job.