i know a number of people who entered as tourist and then once visa came through, got the correct paperwork organised.
the working visa is a sticker in passport, no need to leave and re-enter to activate it, but you'll probably go to macau or shenzen for a day or two anyway while you are here, and when you reenter they will stamp you as 'entitled to remain for work until X date' instead.
technically tourists require a return flight, but i dont think they ask for this very often, but you can always get a refundable ticket so that segment can be cancelled and re-imbursed to your credit card, contact Qantas or Cathay direct for this.
the only other waiting period is for the HKID card, for which you will have to go and queue up for twice personally; once for photo taking, fingerprinting and short interview; then a second time a few weeks later to go collect. take a book as it is a dull experience, but this is only after work visa has been issued and you are here.