The question of "do you need a lock" depends on how likely it is for someone else to gain access to it. If you have a lot of people in and out of the house that could stumble upon it, especially kids, then sure lock it up. If its just you then you are better off being able to grab it fast if needed. It can sit cocked forever, won't hurt anything.
I suggest reading what the NRA has to say about safety here:
http://www.nrahq.org/education/guide.asp
Also, you can learn a lot from taking a concealed carry class at any of the area shooting ranges.