What is fish oil's maximum dosage?

Don't maximize. There is no proven benefit above 200 mg of dha and epa each. Also, it can act as an anti-coagulant so high doses can be dangerous particularly if added to other anticoagulants like aspirin, coumadiin, plavix, (clopidogrel) etc.
It depends. For routine cardiac prevention the recommended daily dose includes the epa and dha components together. This part should not exceed 1200 mg. 800 mg-1000 mg generally recommended. However, if you are taking it to lower your triglyceride level, higher doses like 2000 mg recommended. Not to exceed 4g. There is a higher risk of bleeding at this high dose so a doctor should see you first.