Soda is good for stripping paint and cleaning metal however, it will not remove rust or even etch metal. It might remove rust stains, but not the rust itself. Soda is also very expensive per bag vs. other media. I know this because my buddy has a soda blasting company and we stripped the paint off of my Maverick with it. It left the metal looking as if it came from the stamping plant.
One thing I would suggest is after sand blasting is to hit your parts with at lease 80-100 grit sand paper as the rough texture will not be filled in. I sanded with 80 then 120 since I did not have sand blaster. there are fillers that you can use but you will need to gas off before powder coating.