Few things I've learned in just 3 weeks of freelance:
1. It's easy to feel guilty charging a client high rates while you tackle an unfamiliar project, which requires you spend more time learning than producing. For me, consulting has been a constant tradeoff between taking jobs at high prices where I don't learn new things vs. lower prices when entering unfamiliar territory. I don't know if pricing services according to your ability to execute is best though. At the end of the day, you don't want to find your saying to your client: "I did not execute as promised for whatever reason, but hey I didn't charge much!"
This situation shouldn't arise often if you are honest about your skills from the beginning.
2. Under promise and Over delivery
3. Spec out a project as well as possible beforehand. But agree upfront to a mid-way spec because projects change so fast that you may find yourself conducting tasks you should charge a lot more to do.
4. Build camaraderie with your client but hold your ground if they take advantage. Working with a variety of clients and building a network are advantages of the freelance world. Do you best to build quality relationships with your clients, so they tell your future clients that you are not only a great (insert job function), but also a great person. But I wouldn't go as far as to become so friendly that you feel bad charging them what you'd be making on another project.
To get your idea off the ground, you might consider partnering with tour operators (aka tour guides) that maintain expertise in their individual adventures. That way, at the beginning, you leave the "guiding" up to the experts while you work to measure demand, create a brand and iterate on the value proposition. By handing off the actual "guiding", you can focus on developing the business. Also, I think this method demands less startup capital and/or licenses. While vayable.com does this for small (relative to your past trips) experiences, perhaps a market exists for the grand adventures?
Your expertise would be useful in identifying exactly what people want/need when pursuing this type of adventure, then finding a way to deliver just that. Best of luck!