Good question bloss and well done yangy I don't even know my ring size! Last ring I ever had was miles too big, sent off to be altered to correct size, and came back with completely different diamonds in 
[never again emoticon]..
I think your DS sounds like he has as good a grip on death that any child of his age could handle, and anyway- who knows what happens really? Maybe he is right! I think that having a positive outlook is very good for him at this age because that's all he could handle right now. I know David Cameron's children think of their brother as being in heaven, running around and eating chocolate. 
The questions would floor me though, but I'm sure you handle them wisely. Perhaps a swift 'people are supposed to die when they are very old, unless they have been very very ill' kind of comment would help. I know, personally, that DD's death made me realise life can be very short and it is important to make a difference while you are here.. I hope that I eventually contribute something worthwhile in my time here and succeed because, although she contributed a lot in her time here, she didn't have the chances she should have had, and I hope that DS realises he is very lucky and should really have fun, live but also do something useful with his life. However I'm sure that comes under the 'don't say this to your kids or they will think you are mad and you will mess them up' category..
I'm sure the run up to Christmas is tough on you bloss,my DD first got ill just after Christmas so it's a bit of an odd time of year. I think the first anniversary approaching made me really very down in the run up, the day, and then afterwards because it had gone if that makes sense. Be kind to yourself
I think some people really let me down yangy (as in, they were just nasty!), and some people were just a bit weirded out by the whole situation and thus went awol, and then some nice people just didn't know what to say, so in turn said nothing, or said something stupid like 'oh it's not so bad she was just a baby, would be harder if she was older' etc. I don't expect people to react well because why would they know what to say, so I don't hold it against anyone now, and I don't think less of the people who said silly things, but the ones who disappeared (lifelong friends included) I do think, er, that's bad.