Is serum ferritin different from serum iron and/or total iron??

Yes. All three are related to iron metabolism but have different implications. Low ferritin is a good indication of iron deficiency but normal ferritin level does not rule it out. Iron and iron binding capacity help in differentiation between iron deficiency and anemia of chronic disease.
Completely. It's a measure of storage iron. Serum iron is the elemental iron actually in the bloodstream. A person may take a few iron pills "to be healthy" before visiting the physician and have normal serum iron despite being profoundly iron deficient; only serum ferritin will show the latter. It's actually even trickier. Best wishes.