Not a clue, but I know Nadia told the producers she wanted to be the final housemate to enter and she was.
Other than that, I think they definately put big characters in towards the beginning and end of the show, with all others just in a random order.
BB5 First in was Marco, last was Nadia.
BB6 First in was Derek, last was Kemal.
BB7 First in was Bonnie, last was Nikki.
BB8 First in was Samanda, last was Carole.
All of the above housemates had VTs which were pretty outrageous or 'different', IMO. This year, they put Lisa and Mario in first together, with the novelty of them being the first BB couple. And we had our lovely Kathreya in with a hilarious VT last!