Where can I find information on the rules/processes for severance payments and notice?

I don't know the answer to your question, but I would suggest you might get some ideas if you post this over in Church Administration. This seems like the kind of topic that group might be able to help you with. 

Guidelines for Separation of Pastor and Congregation are found in Appendix B, p. 326, of the Manual of Christian Reformed Church Government.  The guidelines include responsibility of the separating pastor, responsibility of the council/congregation, responsibilities of classis, and a pastoral note.