If you want to work at NOLS. Go ahead and sign up for (and PAY for) their Instructor course. NOLS is a common entry point in to the field for many people, many who don't have significant other experience. OB has employment info on their website as well. You'll learn a lot more about what is required by looking at job postings.... If you're at all into the outdoors, and I can tell you are, step up to the wilderness first responder course. And if you want to be a desirable hire, consider W-EMT.
Being a strong naturalist can be a huge benefit. Typically people with those skills have at least a master's in their field. So if you're just an amature, either be really good at it, or perhaps don't focus your career around the skill.
A long hike like the CDT is definitely not required.
I've been an outdoor guide as my main employment for eight years. It wasn't a lifestyle change, it's been my only career. I'm currently unemployed, partly because of the economy, partly because I prefer not working. For many, it's what you'd guess. Fantastic, often fun and rewarding work. Low pay, no benefits, seasonal work, living in your car, etc etc.
Are you willing to relocate for work? Are you wanting a specific "field area" or are you willing to do trips in a wide geographic area? How experienced and skilled are you? How important is money to you?
Really, not much of this matters. Truth be told, due to low wages and transient lifestyle, most outdoor guiding jobs are entry level and have few requirements for hire. Better ones, perhaps in the REI/NOLS/OB category have more extensive bureaucracy/expectations and provide for a slightly more sustainable job in wilderness travel. The best, expensive, exotic locale guides typically are tops in their fields in many ways (experience, local contacts, graduate degrees, people skills, etc). There is a WIDE range though. I've met guides abroad who frankly didn't know much about guiding, nor have much outdoor experience, yet were able to pull the business aspect together well and find people to pay them.
Other low wage outdoor guiding job fields include: adaptive sports, wilderness therapy, service programs.