Take a class, read a book, install it on a test system, test your application. When you think you're done testing your application, test it some more. If the app is that important, it's worth testing thoroughly.
Honestly (and not just because I am a consultant), you should seriously consider hiring some consulting help for the initial implementation and testing. Unless you've worked with RAC and Linux and large databases quite a bit, building a system so that it meets your stated requirements will be very difficult.
The other piece of advice I'd give you is to build your cluster on a supported Linux platform. Red Hat Linux 9 is the free version that Oracle does not support for any product. If you're building RAC, then you've already spent a pretty significant amount of money on Oracle software, so you should be willing to spend another $1000 to get Red Hat Enterprise Linux for your cluster.
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