Hey Trent.
No "advanced" Birch material but I do have a couple out there just growing.....
Apparently they are not so highly rated Bonsai material namely because they can branch drop without notice..
Nevertheless I've seen some beautiful specimens and see no reason why I shouldn't try and learn myself.
Your tree looks quite nice and definitely has some nice character.
From what I can see it looks like it has a very nice nebari going on for what appears to be a smaller tree?
The pic is hard to tell but I'm assuming there is no silver on the trunk line yet?
I really wish for this (silver bark) on my tree and this is the main reason that I wish to let mine grow..
Bit of info here in case you hadn't read yet:
http://www.bonsai4me.com/SpeciesGuide/Betula.html
Progression and discussion here too:
http://ibonsaiclub.forumotion.com/t11010-birch-only-4yo
Thanks for sharing.