Auburt,
With regard to number 2, I asked this same question not too long ago (nobody knew exactly). One theory is that the pineapple was already cut up (a day or so before), stored in a plastic container, and put in the fridge. But you're right: if the pineapple was cut that night, right before being prepared/eaten, then a child couldn't have performed that feat -- it would have had to have been an adult. To my knowledge, it has never been proven that police found any more pineapple in the fridge, or a container/plastic ziplock bag that may have contained the pineapple beforehand.
Number 3: great question. You know, I wonder if they prepared the food after getting home from the White's party. I know I've done this many times after a party, a wedding, etc. -- because for whatever reason, many times I won't eat enough to get full at a social gathering. This may be common in the sense that, you want to make sure there is enough food for everyone else at the party (i.e. not impose) and that wedding food in general isn't normally appetizing and/or filling (portion-wise).
Number 4: another great question. Was this the catalyst for the attack/head blow? Was JBR discovered by someone as she tried to unwrap a gift?
Number 5: it would make sense that the housekeepers were given Christmas (and the few days prior) off, so the messy house doesn't really stand out to me, but I could be wrong.