A 57-year-old male with low back pain and anemia was diagnosed with multiple myeloma. Hospital tests revealed: Hb 83g/L, urinary protein (+++), BUN 20mmol/L, Cr 200μmol/L, IgG 80g/L, IgA 3.0g/L, IgM 0.8g/L. Bone marrow smear showed plasmablasts + immature plasma cells at 16%, mature plasma cells at 20%. Multiple skeletal X-rays were normal. What is the clinical stage and group?