I would still get the Norton set in full, then add the DMT 325 if needed later...

Everyone starts this with every intention of only getting 1-3 razors and those are going to be new or pre-honed, blah, blah, blah....

Then rad hits and your e-bay account goes nuts, and trust me here, doing e-babies you WILL use the heck outta the N1k and even now and then the N220...
After the Norton lapping stone wears away the back is still good for other uses...