Chemicals are fun! Chemical strippers shouldn't be used if you don't know what you're doing and don't have the right facilities, this is how you get chemical burns and cancer.
Is the rust you're talking about in the cottage cheese of a TIG weld, or at the edges of a lug? If it's a lug, get somebody who knows bikes to look at it for you and see if the rust is bad. Rust tunneling into a lug is bad, and probably means the lug was never brazed right in the first place. If it's just rust in the valleys of a TIG weld, get a wire brush from the hardware store, they're like a dollar. Wire wheel on a drill or dremel works too.
You've already started, but you're going to find out that sanding the tubes is way easy, but doing all the other stuff is going to make you want to kill yourself.
Braze ons come off very easily with cutting tools (big cutting pliers, dremel, whatever) and a file to smooth things down. With sandpaper, you might get it done in time to start collecting social security.