You only need to be activating one of the books. It is suggested you PR 5 books and activate one book completely a week. This would work out to only one 20 minute activation session a day. Less as you move one.
I would say activate one book at a time. If you have the book gel in 5 days or 3 days then start activating another.
I've always assumed that 3 to 10 books meant 600 to 2000 pages. I think it would be fine to PR a single large book. However, I think you should keep to shorter and non-fiction books for the activation. This isn't to say you can't work on activating a chapter at a time in that big text book. The smaller non-fiction books are just probably easy to see success. Having said that, I think that if you have high confidence in your natural ability to exploit the PWMS and you are highly motivated to own the material in the text then you could have great success in PR a big text.
I just don't like to see people turning to PR at exam time to save them. They put a lot of pressure on themselves, and negative emotions (fear) and lack of sleep can block the process. I think that some people can do it and master the system very well, under these conditions, but most will be setting themselves up for failure.
I hate when I get negative. AlexK would have just said DO IT, and Play With It, and See how it works for you. He is right. It can work for you. However, I can help think of all the people I've known scrambling for a life-line when the deadline is charging at them. They are not the people I would say are in the correct state for the PWMS. However, they are the people that have the most to benefit from such a system.
Sorry, I started rambling.
Good luck,
Iam2 
