Changing System Disk?

Hi Mac Pro 1.1 Lastest Snow Leopard, 4 HD’s (1 x 250GB, 3 x 500GB). On HD1 (250GB) I have the system and lots of apps, on the other 3 lots of music audio stuff (I’m a composer). I bought two new 1TB internal HDs, so I’d like to move everything from HD1 (system and else) to HD2, and then install the other two HD’s. I have a new 2 Tetra external HD to aid in the switch, then to become a Time Machine disk. I’ve heard about creating a disk image, but don’t know anything else.

Any suggestions?
Thanks in advance

 

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Thanks!