about the chain coming off, that may be due to cable stretch. If you have been riding a lot, then your cables will slowly stretch, and your derailler adjustment will get screwed up, and it may pop your chain off. no biggie, just take it back to the shop you got it from. they usually offer a free tune up.
About the weight thing, i wouldn't worry about it. places to take weight off are in the wheels mostly, but your bike has a gaspipe steel frame, and that is going to be heavy no matter which way you look at it. I would not worry about the weight, just ride the bike and enjoy it.