In a patient with suspected systemic medium vessel vasculitis and marked hypocomplementemia, what additional workup and steroid sparing therapy would you recommend?

Patient with petechial rash, sensorimotor neuropathy, hematuria/proteinuria, renal infarcts, renal artery microaneurysms and severe ischemic duodenitis. C3: 30, C4: 2.4. ASO elevated 1525. Negative blood cultures/echo and renal biopsy deferred due to aneurysms. Skin biopsy is pending.