Sweet shoes. I wish the mens version looked as nice as those.
I think you'll find that toe clips aren't recommended for mountain biking. I would guess the reason is that they are harder to get out of, requiring the use of a hand. Not easily accomplished while you are going over the bars. In the end, I think clipless is really the only sane option.
When are you ready? I guess I would characterize it as when are you ready to have more control of your bike and to quit being worried about your feet and pedals. Depending on your type of riding and what you are used to, you may never feel ready but I think anyone can benefit from clipless.
It's another skill that you should practice, but doesn't have anything to do with your skill at riding a bike (in a strict sense).