It's pretty much accepted that it's possible to count cards at land-based casinos. But many players will point out that counting cards are impossible at online casinos. In truth, this isn't true. It's perfectly feasible to count cards with online live dealer games. Having said that, much will depend on how often the dealer shuffles the decks. Or, as it's better known, the deck penetration. This is the most important factor and will decide if you'll end up making a decent profit over time.
Playing blackjack as a hobby or pastime is very different than playing as a professional. For a start, you have to make enough money to make a decent living. When you take into consideration the tiny edge the professional player has over the house, you'll need to be playing more or less non-stop to pay the monthly bills. If you want to make the transition from amateur to professional, then you'll need to learn a huge number of playing elements to help you win consistently.