Dentatus,
Definitely get some Club Shirts, more then one is better! Wear them when you're out and about gaming, visiting shops, or attending Shows!!
A Web presence is essential where it be a Blog, Web Page, or even just a Facebook Page to get started, and have at least 2 Members with access to update it on a regular basis! (weekly or bi-weekly is best!) POST photos of Games played with some commentary!!
Set up an email address that all 5 of your current Regulars have access to in order to respond quickly to any and all inquiries.
Print up some Business Cards to hand out when out and about!
Make yourselves familiar with other Clubs or Groups in your local area, so you're aware of the open and friendly ones, or the ones who are not so inclined.
Most importantly once you formalize as a Group or Club be sure your core regular members as well as the part timers are of one mind as to the direction you wish to follow! Let each play a part and contribute to the best of their abilities! As long as you all get along with each other you'll be able to get along with the new guys as they come along!