I hope that I can help you, but I will need to ask you some questions first
When you say Senior, I assume you mean the senior division of your local county science fair? Or are you talking about your state fair? Since the ISEF is not until May, I will assume you're not talking about what you need for that fair yet. Is this correct?
With regards to the log book, it really depends on each judge. In general, a good log book will document everything you've done, including the failures. Judges like to see the process you went through. This helps them ascertain that you really did the work.
I would think that 100-150 pages of research is more than enough, as long as it's not all repetitive.
Sheet protectors can be a good idea if you're expecting a lot of judges.
The main difference between the junior and senior divisions is one of expectations. In the junior division, novel work is great but not required - one can still win with excellent science and method. By the senior division, we're looking for real results and new and novel research. Winners usually demonstrate work at the college level. Winners that go to ISEF are usually working at the graduate student level. Amazing! It's hard to believe, but that's what is happening.
I hope this helps. Please post any specific questions and I'll try to follow this thread.