You can use your springs, and probably plates though you may need an extra 1 or 2 to get right stack height. Not sure if DP has an alloy basket; if so you would be better getting alloy plates. Price is okay, I think.
Alloy plates are the tabbed plates with friction material on them; looks like an alloy basket from here. Not sure, but shouldn't it have a spider spring (I know some slippers don't)
Sorry for my dumbness regarding this, but those alloy plates you're talking about, are they selled separatly? Do they come with the discs when you buy them? And err..... what's a spider spring?
You can use your OEM pack, it's just that sooner rather than later the steel teeth will notch the alloy basket. You can buy an ST4s clutch pack which has the whole caboodle inc. alloy friction plates. However I've had one on order for 6 weeks and still no sign, so I'd be keen to find an alternative source. I think John Hackett sells individual plates but I haven't been in touch to find out if they do alloy ones.
The spider spring is a star shaped tensioned spring that fits somewhere at the bottom of the clutch hub (I'm no expert either!). The Ferraci and Casoli slippers I've had both had them.