I think you'll enjoy both options. They both have spacebeds. However my preference is the later flight, because:

a) it is 747 and the last of 3 flights to AKL that evening so less chance of being totally packed, plus option of top deck (likely to be full) or lower deck (may have this almost to yourself)

b) easier sleep times, dont get woken up quite so early on arrival and also easier to adjust body clock if have flown in from somewhere else on very different time zone (not so long to wait until sleep in proper bed at a "normal" hour to help get over tiredness and any jet lag

c) at this time of year it arrives in a bit of a lull at AKL so can get through immigration quickly, although if there are short delays then may arrive just after the NZ flight (which leaves before but is 767 so slower) and so longer queues, but if longer delay (over half an hour) then again normally no major queues. Note I am assuming your travel is before daylight savings kicks in as my experience last summer (kiwi time) is always big queues for this flight, although may be lucky and express lane open which nicely negates the queue for NZ and Oz passport holders (just need to buy something duty free).

Yes definitely have access to SKL lounge in SIN when flying Raffles Class. It is quite a good lounge, almost as good as AKL lounge IMHO.

Cant help with the other questions, sorry.