Thoughts and questions on starting an LLC to moonlight GIS consulting and web hosting services.

Hey guys, I've worked with GIS for 7 years, 5 years of that involved managing the GIS department for a large quasi-munical water distribution and wastewater collection organisation. My college has similar experience in the public/private sectors and we are really itching to start a small consulting firm in the area. We both have contracts at several municipalities and we would be targeting small municipalities and town/city governments almost exclusively.

My biggest question so far is related to invoicing a customer. I'm wondering if any GIS-centric consulting companies out there have a standard to follow when offering particular services. If anyone has any feedback on the subject I'd greatly appreciate it!