I think a good tank size would be a 50-60 gallon.
Most live fine in fw for about 6 months, then (like already stated) develop red sores mostly in they're mouth, or develop a whitish slime and die.
Try aqualandpetsplus.com
All I remember is they sift through sand and rake out food with they're tiny teeth. They do best with a sg of 1.006-1.012. Can be kept with bumblebee gobies, freshwater flounders(soles), and other peaceful fish.