1 - When in Limbo, go down to where you smash the door with the burning man. Continue through the tunnel, DO NOT GO THROUGH THE SIDE DOORS YET, you will come to the head of the huge demon you killed at end of last chapter. Push it out for Burning Eyes achievement. Turn the corner and the stone is in the fountain next to the Eyes of St Lucia relic.
2 - In gluttony, hall of mirrors puzzle on right hand side.
3 - Descent into Greed, in the tunnel, just before the end, there are ledges on either side. Jump up onto the right-hand side one. instead of jumping straight to the left-hand side, try jumping diagonally left and backwards, this should take you under the archway. Use only one jump to do this and just as you get under the archway press A again to double jump and grab the ledge.