There is no hard and fast rule for trading. It all depends on the situation and your risk taking capability. So no one would be able to tell you about holding time of a coin or what amount to put in to trading. because, that differs from case to case. You need to track the market very well before you can enter trading activities because if you don't track the market well, you will probably end up making huge losses.

Secondly, you need to have patience while trading. Don't get tempted while trading with a particular pair. If you see that you are making loss at a particular trade, and there is no hope for the future, you have to take that loss and exit from that position. So, you need to have the power to face the loss sometime.