Ghosty,
I hadn't forgotten about you - feet have barely touched the ground the last few days. MIL and FIL due any second now, to stay for 5 days so I will be brief.
AS everyone has said, all your fears are perfectly normal (I was convinced I would die in childbirth too...I think that's part of second time nesting instinct, you're subconsciously leaving things in order as you're imagining your dh, holding the new baby, standing with your child at your funeral, weeping by the graveside. Hormones, eh?) Brilliant postings already on most of your worries so I will mostly address the PND. I had it severely with ds1 and was petrified I would get it again. I did. BUT...it was nowhere near as bad second time around. I knew I could and would feel better, whereas 1st time round I couldn't see a light at the end of the tunnel and really thought my life was over. Plus, somehow, no matter how shit you feel, you carry on functioning for your eldest. It may not be the best quality parenting but I didn't disintegrate as I did with ds1. I started on anti-d's when ds2 was 6 weeks old, and things steadily improved from that point on. AND, I bonded immediately with ds2, it took months with ds1.
Plus, second time around, you don't have that psychological shock that you have the first time. I was terrified of ds1, had no experience of new babies, couldn't understand why he cried so much, and the lack of sleep just knocked me for 6. Second time round, still zombified from lack of sleep but at least you know it's coming this time
Your eldest doesn't get as much quality time, of course not, but you are giving them such a great gift, one that (God willing) they will have for a lifetime. They have an ally who will understand exactly how nutty their parents are, and to share all those childhood memories with.
You will be fine. Cross the PND bridge if/when you come to it. You're far better prepared this time around, and you've already learned the greatest parenting lesson..we're all just winging it and pretending we know what we're doing (it fools our children til they have kids of their own )
I have enjoyed DS2 in a way I never did DS1, I adore them differently but equally, and I feel like a much better Mum to two than I ever was to one.
Oh, and not doing this in any sort of order, I had never been away from ds1 til I went to have ds2, and then I was in for three nights. I missed him like mad and he didn't miss me at all..when he did come to visit he was bored after 5 seconds and wanting to leave. I'm sure your ds will be fine too.
I know I haven't covered everything but I've rambled on enough, I think (not good at brief!).
Basically, you will be fine..it's going to happen, it will be hard (especialy those first 8 weeks or so), but you'll muddle through and cope, and you'll even manage to enjoy most of it..honest.
HTH a bit.