Honestly, I don't know much about acid washing, never seen it done or had the need.
But I do know about paint stripper, and how it soaks into the metal. Ive seen how decal remover will cause blemishes in paint jobs even after the metal has been completely media blasted after using it.
So, I would ask some questions about it. Especially since you will need to be doing a lot of welding on this tank and breathing any gases that will be produced from that. Also, I wouldn't be in a big hurry to take all of the paint off of the tank right away, its just going to start rusting on you and will need to be prepped again after fabrication is complete before painting and seasoning the smoker. I would recommend just a good pressure wash and flushing of the tank, and clean the areas you are about to weld with a flapper wheel right before welding. Once you get ever thing fab'ed up and do a test burn and it checks out o/k, then have it media blasted inside and out to white steel.
So have you decided on a design yet?