What is the first step to take to start and maintain a career in network/information security?

I'd have to say this would be learning the fundamentals of information security, and then finding work where you can begin to practice what you've learned. Most people do this by pursuing an entry-level Infosec certification like the CompTIA Security+, SANS GSEC, or TruSecure TICSA (among several others). Since this has worked for many others in the past, it's also likely to help you start walking down that path, at least far enough to decide not only if it interests and suits you, but also if you've got the technical interest and aptitude to do the work involved.