I use a mouse…for any beginner in Zbrush that is fine for in the beginning…but i think when you become much better in the whole Zbrush thing you will prefer a pen more…because basicly everything in Zbrush is done drawing it…even 3d. so the fase when you want to use a pen will come to you when you find out you are much better now in all of it in Zbrush…just focus now on learning Zbrush m8! 
You did a right choice btw to learn Zbrush…now you wont deal like dozends of other 3d modeler before you (like myself) with point to point modeling like in other normal 3d programms (wont name any names) what makes ‘character creating’ such a slow process… allthough it is good to learn the roots from 3d modeling first if you are really new in this and all but…if we are talking about character creating…Zbrush is the fastest way to do it and for me…The Best way.
One thing though because i am still learning this program aswell and didnt see that future in Zbrush…if you want to use your character that you create for animations and all of that stuff…it is best to use a normal 3d program first to create a basic mesh (low polygon model) and transfer that to Zbrush to really sculp out the details in there. example:
http://www.zbrushcentral.com/zbc/showthread.php?t=032885
after you are happy with the model you can switch again to your normal 3d programm for furter work. (So please DO learn a normal 3d programm for all the other stuff besides character creating )
Well thats all…hoped that helped a bit.
Dont only take my word for it though.
And last but not least Welcome to the Zbrush forum! trusth me you will be a Zaddict in no time 