Recommended file distribution


Based on everyone's experience, is there a recommended way to distribute files related to Logic that works the best to avoid system resource problems? For example, having the main boot on the system hard drive, plugins and VI's on the main hard drive or an external drive and samples on an external drive.
Is it "ideal" to have everything on the main system drive if the computer is basically dedicated to Logic and has a large hard drive?
Does it depend on the plugin or VI?
Is it best to save projects to an external drive?

The reason for my question: I plan to very soon purchase an i7 iMac to dedicate mainly to Logic and I believe I can afford 8-12 GB of RAM and the 2 TB internal hard drive. I use a Duet as my interface and I am planning to do home hobbyist type songwriting/recording. I have been learning Logic 9 (using David Nahmani's book) on my MacBook Pro and have no projects started yet that I would have to "port" over. I want to start fresh with the new iMac as the hub of my home studio. Could I do everything I would want to do without an external hard drive (which I would only have for Time Machine backup) with this type of setup or in regards to Logic, is an external drive really recommended for certain things?
Basically, if you were setting a DAW up from scratch, how would you arrange your files?

Thank you in advance for your advice/opinions.
Don't worry, I won't hold bad advice against you. Any suggestions?
Oh - never mind. I found the iMac string on the Logic 9 discussion thread.