Personally, I think it would be a good idea to do a few lessons first to see how you would 'get on' with flying, I appreciate your enthusiasm and I wish you well, I've no doubt you'll do OK, But why waste your time and money on doing the ground exams before your
first lesson, (and I mean that constructively), you have plenty of time to do your ground exams during your training. It's a good idea to read up as much as you can tho', your FI will guide you through the right way to approach the course, but as I say, reading and learning before hand is not a bad idea. I wish you well and keep us informed of your progress.
