Is there a general rule of thumb as to how many classes, interfaces etc should go in to a given name space before the items should be further classfied in to a new name spac
I don't know of any rule of thumb for the number of items, but those kinds of rules tend to be over-generalized garbage anyway. Make sure there is a logical connection between items in the same namespace. If a namespace is getting too crowded (unlikely, I hope), or the things in the namespace are only loosely related at best, consider breaking it up into multiple namespaces.