Icy,
Jia you!!! Yes, there was a few times when my girl used me as human pacifier. I think it's very common? You do full latch on? Give your boy more attention as much as you can, and let your MIL/maid handles your baby. Probably just do the essential must do with your girl, ie, feeding. The rest can leave it to others, until your boy gains back his comfort and security, then you can divide your time between the two. And create opportunities for the brother-sister bonding helps too.
Kitsune,
I would think it would be best to have #2 when #1 reaches 3 years old. To me, the 0-3 years period is the most critical for a child, when he needs a lot of attention, a lot of guidance, love and care, and this is the period that they learn the fastest and most efficient. The Chinese says "san shui ding ba shi" (translation - your characteristics at 80 years old have already been form when you are at 3 years old). Now I can only give 50-50 (okay, honestly, not quite 50-50, but I try) to HR and XY. When things didn't go on smooth, I did question myself why have #2 so soon. But then, cannot u-turn liao, so I am trying my very best to work things out, so that I am still able to give them enough attention for their critical 0-3 period. Just my own thinking.