a few comments:
1: If it's a noise just like a noisy tappet (cam follower) that comes and goes as you rev the engine, chances are it's the variator. I've mailed a tech article with photos to this website on replacing the variator and camshaft, so it should be up soon (I hope).
2: if it's a blocked injector, the engine note doesn't change when you pull the plug off the bad injector. If it's okay, revs should drop a little. Dunno about the popping or sucking sound.
3:You can get an oversized sump plug (M20 thread) from the dealer. It's a common problem. Alternatively you can have a Helicoil put in and reuse the old plug. For both options I would take the sump off, to prevent bits of metal swarf ending up in the engine.
4: the plate holds down the coil packs I think. The coil packs have spring loaded contacts on the spark plugs, so you want to make sure the coil packs are secure. Maybe someone can have a look at their parts CD (I want one!) to see if the plate is available separately.
5: no idea! Sorry....