There are many benefits and disadvantages to capping your FPS. Capping your FPS saves energy and resources on your computer. Keep in mind however that it is not vsync and will not prevent screen tearing. Capping your FPS is best used when you are on a laptop, a computer that overheats easily, or...
After locating the GameData folder and selecting it for the launcher, go to that same folder again and double chack that the "MBII" and "MBII_Launcher" folders are there. Also how is it not working, will it not launch the game, or just not download?