I'd try a little of both seeds and transplants. Radishes are very easy to grow just about anywhere. When my kids were little and I was short on gardening time, I always liked salad greens (like lettuces) and radishes to see quick results. Transplanted tomatoes are very easy if you get them started from the greenhouse as tomatoes have few pests. Peppers are also easy and fun. Strawberries bought at the point they are already producing berries give some instant gratification and would work in your climate. And for fun, edible flowers like nasturtiums add nice color and can be bought from transplant. I don't have too many other suggestions because I'm not blessed with living in your warm climate, so I'm not sure of some plants that work for me here (USDA zone 6a) not working with the heat in your region.