Go for Botia Striata!! I have had both sids and zebras and I love them both, but zebras are cheaper and don't get that much bigger. I had some for years and years that never got more than 3in. They will be fine in a 30g, and personally I would get at least 5. Loaches do better with 5 or more, and I think as long as you keep on on your water changes you would be fine.