Should the urine tests still be performed even though the plasma free metanephrine has been done?  

Often no. The plasma has more sensitive and more specific and generally adequate (better) in most situations. It would depend if the doctor is more worried about a false positive (finding pheochromcystoma you really don't have), or more worried about false negative (missing the disease when you really have it). Your doctor would decide based on your symptoms which is the bigger worry /risk.
Excessive hormones. Plasma levels are points in time so often a 24 hr catches total excessive production.