Sharron, I did a quick search on Google Scholar using various key words but did not find any relevant articles on the topic in the research literature. I would assume how much income you can make depends on the hours you invest per week, the size of the bets, your level of ability at skills like card counting, the form of gambling (poker, blackjack, sports betting) and luck. I would also assume that the level of income one should be making in order to consider it as a career would be one that successfully allows you to pay all of your expenses (house, car, education, etc.) with enough left over to continue gambling.
The Gambling, Gaming & Technology Use Community of Interest brings together addiction and mental health service providers, researchers and subject matter experts in the fields of gambling, technology/Internet use and video gaming to collaborate and share knowledge on emerging trends and clinical best practices.