I tried my hardest to find the key in that level, I'm not sure which one it is, but it's a large level.
I might just be blind, but I couldn't find it after a good 5-10 minutes of just running around the level.
Giving the player a compass, or map of the level would be a huge help in letting them plan their route. And a dodge roll would be all you'd need I think to give the player that edge to escape the ghost in a tight space. The biggest thing imo was the hallways that weren't big enough to get through without picking up the coins, they were basically a game over if the ghost was behind you, forcing you down the hall.