The medical care is one aspect- HKID holders get free treatment in the government hospitals (similar system to NHS) but tourists don't, so if you dont have a HKID, make sure you have really good travel insurance that covers extended stays. If, heaven forbid, you got appendicitis and ended up at Queen Mary's, you do not want to find that your travel insurance only covers 2 week trips. In any case, you will almost certainly have to pay medical costs upfront and reclaim so make sure you've got a decent limit on your credit card. Your bf may get medical insurance with his work, but it's unlikely to cover you, as you're not officially his dependent.
The other issue with no HKID are things like you cant be on a residential lease, you can't be on utilities, and therefore you have no proof of address. It can be hard to open a bank account- I suggest that if you're with HSBC, you open a HK account from the UK before you go - and almost impossible to get a credit card. You can't get a phone contract, although your bf could get one in his name and just give you the phone. Once you get a job, you'll get a HKID, so it's just a temporary annoyance, but one nonetheless. It is also theoretically illegal to look for work on a tourist visa, although not illegal to accept a job offer- in practice everyone does it, so dont worry on that score, just be aware of it.
The only other thing to consider is that some employers will have a strong preference for candidates who are either on dependent's visas (because they are permitted to work- employer doesnt have to sponsor) or who already have a work visa (Because transferring is much easier than applying from scratch). If you work in a sector where there is a clear skills shortage in HK or a high % westerners in the workforce (e.g. you're a lawyer in a magic circle firm or an investment banker), then this shouldnt be an issue. However, if you work in a sector where the employer can hire locally quite easily, then it could be harder, because they need to prove that they have tried and failed to find a local with that skill set. It's quite a process and some cant be bothered with it.
Another thing I thought about- if the company isnt paying shipping, consider buying your furniture here and just coming over with excess luggage. A friend of mine did that and it worked out cheaper. Also, western furniture tends to look oversized in HK flats, so king sized beds and 8 ft sofas are best left in UK.
Electric sockets and voltage are the same, so electrical stuff will work in HK.