I know I've replied numerous times with recommendations about buying specific Macs, or types of Macs; search the board with regard to this.
As for the peripherals: DSL will work wonderfully well with OS X. I don't know about you, but here we have to use MacPoET to sign into our Earthlink DSL under OS 9. When I haul my iMac in and plug the DSL into it with OS X, it works completely transparently, and automatically connects to the service.
If you don't want to replace your current hard drive, I recommend you buy a Firewire enclosure and place the disk within this drive. USB is incredibly slow for hard drives, and you'll get much more responsiveness out of a Firewire enclosure. However, hard drives are relatively cheap, and you can get in excess of 100 GB for barely over $100.
You probably won't need the external CD-ROM drive (it's a CD-ROM drive, right? Not a burner?) unless you want to copy CD's directly without needing to make a disk image, as I believe all Macs currently ship with a single burn-capable optical drive. However, as I stated before, USB is very slow and you'd probably only be able to achieve 4x write speeds when copying CD's. There are advantages, though, like being able to directly copy CD's (as I mentioned) and being able to mount more than 1 CD at a time (something I do rather often). You can keep a commonly used CD, like a game CD, in one drive and put another CD in the other drive when you need to get to the data stored on it.
The Superdisk will work fine. If this is your choice of removable/transferrable media, like vs. Zip, and/or you like to work with floppies (why, I have no idea), then the Superdisk will work wonderfully well. And you won't get any annoying messages that the drive works like with Windows XP.
If you have any more questions, I'll be happy to help.