as someone who works with acids regularly, smell is not a good indicator, as many acids are non-volatile.
Cleaning with baking soda is a good idea because baking soda is basic and will neutralize the acid while you clean. If it were me, I'd clean it with saturated baking soda a few times (this will require several boxes of baking soda), then rinse it with soap and water a few times, and then just water a few times.
If you want to be really sure all of the residual acid is out of there, take a pH reading of your water from the tap, and the water after filling the carboy. Any dissolved acid will noticeably lower the pH since water is not buffered. Similarly, residual baking soda will raise the pH.
Acids in that large of a container are probably either hydrochloric, phosphoric, or acetic. The first two are very caustic, but harmless once neutralized, as they become just salt and phosphate, respectively. The last is basically very very concentrated vinegar, and will add a noticeable taste, though it will also smell like vinegar before you can taste it.
Nice score, Steve!
