I use walnut media first for a fast clean. actually I use walnut shells these days but that is a deviation from normal.
I do a finish run with corncob esp when I want the parts super shiny.
Whether or not it is necessary might be up to the individual, its just what I have worked out.
I thought acid bath was the way to prep for plating purposes?
Or is that just for commercial stuff.
I'm no expert 
sorry I didn't explain properly, I am using buffer and tumbler after nickel plating.
I have only just started using the tumbler on the plated parts because up until now i have been doing large, easy to get at pieces and have been getting a mirror finish with the buffer.
