1. Don't you mean "dependency"? In the example, A class is dependent on B, and it's B that has to be modularized.Thus, bottom up approach is possible only when the dependent libraries are modularized already.
2. By being put on the module-path you mean that's it's either a part of a named module or an automatic one? Is this identical with "being modularized" mentioned above?Effectively, when bottom-up migration is complete, every class/package of an application is put on the module-path.