Seems more logical to me to wait a little while before you worry about the exams.
You say you've noticed that quite a lot of people are taking the exams before their flying training. I think I'm right in saying that these people are generally planning on doing an intensive course to get their PPL in a very short time, often in America. Many people who take this route recommend doing the exams first, because there isn't enough spare time on the course to do all the studying that's required. But if you're flying for an hour or two a week, as most of us do, it's really not necessary to do any exams until you're at the stage where you might be ready to solo soon. This will also mean you'll have some practical experiences to back the knowledge up with.
Good luck!
FFF
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