I'm just getting back into fitness. Bought myself a dumbbell set and am starting a 3 day split. Though the program I found didn't include any core workouts. After doing some googling I was gonna try ab roller, plank, and side plank. Are those enough, or should I add more?
Sort of. You can't really do conventional deadlifts with then, but single leg deadlifts are viable, and imo the only dumbbell deadlift variation worth doing. Plus, they're very challenging, so you won't outgrow the weights you have available to you so quickly. They aren't the same as reg deadlifts, and once this pandemic is over I do strongly recommend you get a gym membership so you can reap the benefits of barbell lifting.
As for abs, planks and its progressions are fine choices and will absolutely suffice. However, if you're like me and begin to find them fucking boring, go get an ab wheel. It's more dynamic and enjoyable than holding a fucking plank for however long. It's important to note that ab wheels are very challenging, and that you're going to want to google the progressions and proper form for it so that you don't hurt yourself. Depending on the core strength you start with, this might mean starting on your knees and only going a short distance at first.