Coral Painter mimics traditional media and does it well. Some people prefer it. But to be honest I wasn't that impressed. Mind you the last time I used Painter was version 7 (like 7yrs ago) and I have been hearing good things about it. --But trust me when I say, If you can't digitally paint in Photoshop then you wont be able to in Painter. Too often people think if they have the right program, the right mouse, the right pose, the right tablet that they will suddenly be struck with genius. Let's face it; thats not how it works. As for a tablet. You dont need one. I know it sounds crazy but there are shortcuts in Photoshop to speed up the process. Also if you can do it on a mouse then you will be able to do it with a tablet. That being said a tablet makes things easier; therefore if I was to buy one I would get the Wacom Intuos4 Medium Pen Tablet which is about $370.
If you want to learn digital painting then start off like you would any other kind of media. Concentrate on light and dark. Painting in monochrome (shades of white and black). Paint spheres, and cubes, cones. Then do simple shapes that you can construct from basic media structures (spheres, cubes, cones) like a book, a cup, or a bottle. Follow that with moving onto more complex shapes like fruit, vegetables, and flowers. Just keep building on what you already have. And keep it monochrome. Because once you can paint in shades of black and white there are techniques that will let you color it later on.