Pull back
You don't need to have done the exam to start the training, however the material in the books is terribly dry.
Further more, going through it from the text alone with no experience just confused heck outa me.
For my thoughts, I feel doing the exam in the middle of the course makes it easier (course and exam) because you can relate the text more readily to what you are doing. Beyond this I am the world's worst studier and knowing for example I will be doing NDB tracking next forces me to learn about the damn things!
In essence, having an idea as to what you are pinning the knowledge to practically, makes it easier to remember and easier to implement. Wait until you read about intercepting NDB QDM's and QDR's.
It is however worth speaking to the school where you intend to do the training as they may have some more suggestions or even a preferred method.
Obs cop