OK. Basically
you've not done any prep for export which is why it's breaking. So to answer your original question; so far as I'm aware there aren't any limits associated with the *.md5mesh and *.md5anim files themselves (because they're basically a formatted text dump) so that generally is never really going to be an issue.
Have a read through the posting linked to above - I had to do most of what's discussed there to export a working set of files. But generally you need to assign vertex groups, an armature, properly UVW unwrap the mesh and optionally, possibly change the orientation and position of the mesh and armature (which means that you need to use 'Apply' and set their respective location data where necessary) - I had to do the latter to make working on the file easier, Blender doesn't play nice when models are rotated around 'odd' (to Blender at least) axes.
Additionally, you may want to look at reducing the polycount on the model, it's very, very *heavy*, you could probably get away with maybe half of what's been used at most - obviously spheres are pretty heavy items normally but there is a lot of 'waste' (in the sense that there are a lot of surfaces present which don't really do anything in relation to helping determine shape or form).
Also watch out for the use of 'open' surfaces. Ideally you want those leg protectors to be a solid double-sided ('closed') mesh rather than single sided as they are at present.
