1) There is no player-proof storyline. If you create it, they will hose it beyond all recognition. In a good way, mind you, but don't plan a storyline's conclusion, because you have NO IDEA what the players are going to do.
2) There is such a thing as a "timely" death. This is the result when a character gtes killed in such a way and at such a time that it convolutes the ongoing plot so much that it actually resembles the plot as you had originally designed it. I've seen this happen more than once.
3) You can't please everybody. Really. You can't. You may think you can, but somebody's always off grumbing in the corner. Make a small number of people happy and you'll have a small game. Make the majority of people happy and you'll have a big game. Make nobody happy and you'll have to actually get a life on Saturday nights.
4) Assume that any item that you give to a player character can find its way into the hands of any other player character. If it's something powerful, think to yourself: "Do i want X [the last person in the world who you want to get their hands on this thing] to get his hands on this thing?"
If the answer is an unequivocal "No," then don't give the weapon to anybody. Because it just sucks that bad.