What are some good concrete metrics in defining remission for waldenstrom's macroglobulinemia - in terms of bone marrow analysis and IgM level?

50%, 90%, 100% Con?rmation of response in wm has been adopted from response criteria for multiple myeloma. See http://www.Iwmf.Com/docs/ghobrial_clincial_trials.Pdf especially see tables xi, xii. The treatment of wm is aimed at control of symptomatic disease. Risk/benefits of various therapies are highly individualized based on patient and disease characteristics.
CBC and IgN. The best parameters are the CBC which should be normal and the IgM level.
A good Oncologist. I would imagine when your bone marrow aspirate/study comes back "normal"; and your blood counts normalize that is a very, very good indicator of remission. Of course; let the expert(hematologist/oncologist) make the final determination. And congratulations! if you are indeed in remission.