1. 6 hours seems like a safe interval of time, though I would be interested in knowing how the two interact.
2. Nothing really "produces serotonin" other than your body. Consuming 5-htp, a precursor to serotonin, may boost serotonin levels in the body. Where did you hear that ginseng increases serotonin?
3. Who says we need to take anti-depressants? They clearly aren't for everyone, especially with all the safer alternatives out there. There are so many out there, like the ones you mention and Rhodiola rosea, and better diet, exercise, and jeez, the list goes on and on.