Good luck with the job and fingers crossed you find some things you like when you get here. It's a fun city and you can have great times here, but obviously there are differences that you need to acclimatise to and there will be some things that will drive you crazy.
Food wise you can pretty much buy most regular UK things here, there are plenty of standard supermarkets that almost entirely cater to international food desires. Even nice bread can be found and bought easily, although admittedly most supermarkets standard sliced bread is not what you'd be thinking of. There are also more expensive specialised supermarkets that stock more obscure items. I've not found anything (other than goats milk) that I bought back in the UK that I can't get here.
For living, as a first timer I'd definitely say look in Mid-levels or Soho and Sheung Wan areas, you'll gain many of the benefits of living in Hong Kong (very short walking commute, busy easy social scene and all the Western home comforst HK has).
Public transport is cheaper, faster, more frequent and more reliable than anything in the UK (taxis, buses, minibuses, trams, tubes, trains). Public transport users in the UK are either very polite and aware of those around them or psychopaths one blink away from a raging death tantrum, here nobody gives a rats arse about you or your comfort, but they won't potentially kill you either. Pros and cons.
Electricals are not significantly cheaper here any more so bring anything you are still happy with, especially as someone else is paying. Anything you have that is old or you've thought about replacing you may as well wait and buy new here, with some hard bargaining you can fnd a deal on a newer product, just don't think it's the electrics mecca it once was.