A rule of thumb I see often is that as a freelancer you would need to divide your target for the year by 1000 and that would be your target hourly rate. So, you would need to look at charging $50 / hour for freelance work to hit 50K per year.
From my experience, that's about right for freelancing and that's about where you should be charging if you are decent with Wordpress. I know of other developers who charge at least $50 / hour and don't know a lot of PHP or even JS. All these developers do all day is configure WP sites.
That said, charge what you think you can charge. The difference between $50 / hour and $80 / hour might simply be what you ask for.
Realistically, the size of your digital Rolodex and your ability to sell is what's going to allow you to hit your target rate. Start networking like crazy and saving as much as possible right now. Hit Twitter, LinkedIn, Wordpress forums and any other networking channels you can find to see the conversations and hook up the jobs. As a digital nomad you would be at somewhat of a disadvantage because you wouldn't be able to establish yourself in one location. That's not to say that you need to work with local clients, but it only helps if you can do it.
You could also hit sites like Odesk and Elance but you have a lot of competition there with Wordpress. You will need something which will allow you to stand out. The more niche and the more you can stand out the better. If you can stand out, then good potential client won't even look at the competition offering to work at $15 / hour.
So, aside from networking, you need to do whatever you can to try to establish yourself as an authority. Create a site, write articles and contribute to the community. Work to make a voice which other WP developers will take seriously. Continue to learn WP and read as much as you can to find out what people are doing to push the envelope with it.
You could branch out into other areas aside from WP, but you should start with your strengths. You could focus on HTML / CSS but combining that with Wordpress will give you a more niche target.
Try to save up at least six months living expenses before you hit the freelance circuit.
Hold off on travel until you have had a chance to get solidly into the flow of bringing in work. Also, freelancing while on the road is difficult. You might benefit from moving somewhere with cheap living expenses though.