The longer you wait the lower the chance. Not sure where you live but where I am they are already pretty hard to come by in shops. After Black Friday I think it should be pretty much impossible, as all shops will offload their old stock.
That's totally a personal decision (I prefer the look of the fat one myself), but you may have a harder time selling a fat PS4 than a slim one down the line.
Those in the shops right now are likely 5.55.
I don't know anything about this specific bundle, but if there's a risk it doesn't come with 5.07 you may want to take the safer route. Also please note that 5.07 is a tricky firmware, as there is no recovery firmware for it - if something goes wrong and you mess up your system with homebrew, you'll have to update to >5.07.
In my opinion CUH-7016B is pretty much guaranteed to have 4.70 or lower.
Thanks for the response. I just found a second hand slim 1tb with 4.70 for a decent price. May I ask how probable it is to mess up with homebrew?