Is the general term small business opportunity trademarkable?

No. One good example of an attempt to copyright a general phrase is Fox's lawsuit regarding the phrase "Fair and Balanced." Fox lost the suit because terms like this can't be copyrighted. Copyright and trademark law sometimes overlap. Contrarily, even though copyright wouldn't protect something like a short phrase, the trademark could still become enforceable, over time, through a concept known as "secondary meaning". However, the general rule is that a trademark must be capable of uniquely identifying the source and quality of goods. The more common or descriptive a slogan is, the less protection it gets you. The more suggestive, unusual or abstract a trademark is, the more likely it will be protectable as your individual trademark.