Ahamad, i suggest too that you take the IELTS first so could have a better idea of your points.
The advantage of not taking IELTS first is that you do not have to spend money right away. It's painful in your pocket when application is rejected.
The disadvantage of not taking IELTS prior to application is that you will be pressured to get the full points if that's all you need to mark the required points.