HaoningW, in answer to your last question its a matter of preference. As each artist is unique so are we in our work ethics and efficiency. You may find doing ten small sketches/compositions or paintings a day is more interesting to you or appealing and if it is great! other times you may find taking a few days or weeks on a single painting and taking your time will really make progress for you.
What im getting at here is we can show you the path, but the map,the backpack and even the steps you take are down to you dude.
Never Attempt the Possible;attempt the impossible and even if you fail,you'll fall among the stars.