I'll try to answer your questions as best as I can in consecutive order...
Prepackaged Material: 3rd party training providers have material for both the written and the lab. They typically are different packages and have somewhat different material due to differences between the written and lab blueprint. Exclusively studying lab material would not be a recommended way to study for the written but much of the material is the same so it doesn't really hurt either.
Outdated content is surprisingly relevant still. Many topics on the current version of the lab are very outdated. Some of this is due to technology moving forward and some of this is to provide design environments that complicate routing protocols and other technologies. V5 of the blueprint sees most of the outdated stuff get updated but understanding the fundamentals of "why it is there" will go a long way into understanding what you need to know. Much of the "recommended reading list" might change due to the new lab version. You are starting at a weird time and almost 100% of the material out there is directed at v4 currently. I don't know of any major training provider, with the exception of Cisco's 360, providing comprehensive training on the new version of the test. If I were to give advice on where to start for the written, it would be the official certification guide (Amazon Link), and Doyle's TCP/IP Vol 1 (Amazon Link) and 2 (Amazon Link) as a more detailed dive into some of the topics.
Regarding difficulty... The written is nowhere near as difficult as the lab. It simply is a pre-qualifier to ensure that you have enough base knowledge to be scheduling the lab. The best way to describe it is that it is a mile wide and an inch deep. It covers many technologies but none of them in great detail. Functionally, I considered passing the CCIE written easier than 2 of the 3 CCNP tests.
If I were you this is what I would do:
1) Start with the blueprint as a guide. This is your reference for what to study and you need to know the topics on it thoroughly.
2) Read the certification guide cover to cover. Really understand the theory behind the technologies. Back this up with deeper dives into the TCP/IP books and further reading on blogs for a different perspective.
3) Connect with a community of network engineers who have done this before. It is a long and time consuming process and many of them are more than willing to help. I have found twitter to be invaluable for this (connect with me there if interested). Do not be afraid to ask questions, this is a very difficult thing to do.
4) Don't focus on the lab too early. The two tests are completely unique. The written is a theory test like all of the ones you have taken so far (more so as there are no simulations on v4 at least). Worry about the lab when you are done with the theory. You will find you need to forget some of what you learned for the written and that can be really confusing when you're studying both at the same time.