I have a wind-up drum for my RPK, and seeing how much movement must occur in order to ensure adequate feeding, I would be very hesitant in using one with a constantly wound spring. Also, you'll probably need a hydraulic press to load the last five rounds
I would stick to the normal style they've been using for the past half-century. Winding it up only takes a few seconds.
As for normal mags, you should be fine with anything, whether they're steel, polymer or Bakelite. You'll most likely get a large amount of mag wobble with steel mags (mine does) but I prefer them than polymer mags (but then again, I haven't used Bulgarian circle 10's, which are supposedly fantastic). Also some polymer mags may be a little on the tight side.
Right now - you'll be best off with whatever you can get your hands on
