They are usually 8mm and sometimes 10mm. a
The "little disc" is a crank extractor (I am a Shimano guy, so Campy people please correct me if it is different). Leave it in and back the allen bolt out. The allen bolt will push on the cap and push the crank off.
The real deal though is that nowdays bottom brackets are sealed units. There won't be anything to lube if it is a modern bike.
The Park tool website is a very good guide to maintenance and tools.