10.6.8 to Yosemite - upgrade/migration questions

[mosk22rte]

I'm a looooooong time Mac user looking to upgrade an original Mac Pro (1,1) from 10.6.8 to Yosemite. I don't need any hand holding w/that part of the process, but I could use help on my overall upgrade strategy for upgrading this particular machine.

Current Mac: Mac Pro 1,1 running 10.6.8. I currently have a lot of data spread across 4 large HDDs, including a large 1TB+ iTunes library on one of the secondary drives in this machine. Due to hardware limitations I cannot upgrade to Yosemite directly on this machine.

Target Mac: I have a new-to-me Mac Mini 5,3 (2011 Mac mini server with a 2.0Ghz i7 quad core cpu) and 2 x 1TB internal HDDs. I will also be using all four of the drives from the Mac Pro with this machine in an external drive tower, connected via either eSata or USB 3.0.

Tools I have that may help:

• I have a portable 2TB USB drive that I can use as a scratch drive.
• I have a licensed copy of Carbon Copy Cloner, if that helps.

What I need is a "best practice" suggestion for how to do a migration/upgrade of this scale, where I can't upgrade the OS directly on the source machine first. I am especially concerned about screwing up my iTunes content, as I have a lot of media I've purchased that is tied to the old machine. The old Mac Pro was basically our media server and workhorse, but it is time to put it out to pasture.

FWIW, I plan on reusing all of the hard drives in the current machine in the external drive bay of the new machine (with their data as is, and without reformatting). The new machine has a pair of 1TB internal drives, while the current machine has drives of 2TB (boot drive w/OS), 2TB (my iTunes library), 1TB, and 1TB. I'd like to put Yosemite on one of the new internal 1TB drives.

Thoughts?

Thanks!