Oh boy.... ready for this?
I'm a bowyer so I'm pretty familiar with wood properites, stress, and seasoning. I'll have to look more into what woods can be used but I'm thinking hickory and oak would serve admirably.
Oak (Japanese White or Red Oak) are traditional woods, as are a range of more exotic ones, such as Sunuke. Hickory has become a staple for North American bokken makers, as it shares many of the same properties as Japanese White Oak.
That said, I'd still recommend waiting until you got some experience in what makes a good bokken, before trying. You'll get a sense of the balance required, the "feel", and so on, which you won't have yet. Intending no offence, but you are still in High School, so I'm not going to be so sure of your exposure and seasoning (ha!) in terms of woodworking.
Different Boken? Are you serious? There is just no end to this diversity! At this stage in my life, moving to japan isn't really an option, nor would I want to even if I could. Is it possible to learn just from seminars? The closest school is at least 4 hours away.
Oh, absolutely different bokken! Here's a small taste of some of the variety found:
http://www.bokkenshop.com/category_s/43.htm
I wasn't really being too serious with my comment about you moving to Japan, not at your stage and age, but the important thing is to realize that that might be your only option when it all comes down to it. When you mention the closest school as being 4 hours away, which school is that? Do you have a link to a website?
Learning from seminars, well, yes and no. Attending seminars, and continuing to work on what is learnt there as part of a study group is feasible, but learning from seminars exclusively, I'm less sure of. The majority of training and learning is in keiko (practice), and that needs to be kept up inbetween seminars.
Also one last requirement for a school that may signifantly limit my choices, IDK.
I'm a Christian and I feel very uncomfortable with any of the 'eastern myticsm' or 'Chi' stuff, so if there are any schools that focus more on the sword and technique than the internal part of things, that would be kind of mandatory.
There aren't any that will make religious demands on you, demanding that you worship anything other than your own choice and faith, however they will all be highly influenced by the religious environment in which they grew. Schools such as Katori Shinto Ryu have a lot of Shinto and Buddhist influence (a particular form of Buddhism known as Mikkyo), Hyoho Niten Ichi Ryu is intimately linked to the Buddhist Sutras in order to understand it's deeper levels, and so on. The point of learning a Koryu is to learn their approach to everything, from the way you use a weapon through to the way you live your life on a daily basis, and the way you think about things. If you can't reconcile that, then Koryu won't be for you, as your personal biases would come in as a corrupting influence on the Ryu, as you really can't pick and choose which aspects of a Ryu you'll follow, and which you'll ignore. It's really all or nothing.
However, something like Kendo can be good that way. As it's dominantly a sporting approach, there isn't the need for much examination on the spiritual aspects (don't get me wrong, they are certainly there, but you can be more selective in which you adopt and which you don't). Same with Seitei Iaido. But I would like to point out something... none of the teachings that you seem concerned about actually conflict with Christian belief or philosophy, unless you decide they do. In Japan it's considered normal to follow a range of religious observances, with no conflict at all. Additionally, concepts such as "Ki" (that's the Japanese pronunciation, by the way) can be thought of as a expression of unified intention behind your action... it's really not much more "mystical" than that. But frankly, if you're wanting to avoid "Eastern mysticism", why go for an Eastern art? It's going to have aspects of an Eastern (in this case, Japanese) heritage and belief system. It's a bit arrogant to insist that they don't, really. It'd be like my turning up at your church for the social gathering, but asking that you don't talk about any of that God stuff, as it conflicts with my beliefs. It just doesn't make sense.