How important is it for me to take my bike to the dealer for the initial service.
I really don't feel like spending that much for something I know I could do myself. Will it void my warranty?
Check your warranty. It should say wether it will or not. You can do your own maintenance. Check the Maintenance Schedule on the main site.
Search.
http://www.gstwins.com/forum/viewtopic.php?t=20521
When I bought a new Honda the first service was free (in UK) obviously I had to pay for the oil. A couple of years later with the GS is was not free but only a nominal sum. It is also a very good opportinity for you to go over the bike and get things done. The first few hundred miles can shake out a lot of bolts and screws, those on the front wheel gaurd are notorious.
Check you bike over any raise all and any issues that you are less than 100% happy with. You dont want to be taking wrenches to a bike under warranty if you can avoid it.