I think you can do away with the RAID and journaling file systems for the web farm. It is load balanced so you should treat each server just like a harddisk. Therefore using Linux for the web farm is ok besides I dont think Solaris has anymore advantages to Linux in terms of running aolserver.
Invest heavily on the db machine. Solaris + Oracle should do ok. Buy the baddest Sun box you can. Get the best people to continue to keep the site in shape. Investing heavily on the initial deployment is not as important as looking at how it will run once its deployed. Policies should be important too, like when to upgrade, how often log files are checked etc. People are the key components your Sun box with a average admin can be beaten by a good admin with only intel boxes.
Code movement/management will be also key since new code can bring down the site.
Maybe you can check back the client again after your study, a lot of this clients demands this outragous uptime where they really dont know what they are talking about. Especially when the bottom line comes out... for example for 10 min down time you just spend 100K for 5 min down time you spend 500K. Once the client see the figures they will decide what is good for them, there is no unlimited budget espcially these days budgets have shrunk.
