The difference is that "decision" is a mental process. To make a decision always requires thought. A "choice" does necessarily require thought. For example, you could make a choice by flipping a coin. You could choose a cookie by reaching into a bag of cookies and grabbing one at random.

Both the same but we tend to say decide when we need time to make a decision. Choose and pick which are synonyms are used more when we know what we want and can make a quick or instant decision.

They are synonyms, so sometimes the meaning is the same, but often we use "decide on" if we want to comunicate that there has been more thought prior to the choice/decision.