There are a ton of posts about the MR, with lots of good advice, on this board. Scroll through, or do a search to find them.
Choice of helmet, or no helmet, is a personal one. Bob R and I had an interesting discussion on this topic on our last climb (you'll have to hike/climb with him to find out what his opinion is). My decision making was influenced by the fact that a good friend was killed in a climbing accident in the Alps, despite the fact that he was wearing a helmet. (I own a couple, but they usually don't go on unless I'm told that I can't climb without it.)
Which brings out another comment: I been in a few known rockfall areas where I've seen climbers, who are tired, with there heads down. (I watched a climber on Shasta take a baseball sized rock to the chest below Red Banks, despite the fact that I was yelling at him for a good 15 seconds, because he wasn't paying attention.)