Hi,
I have precisely no child care experience but I moved to Malaysia from the UK in March so I wanted to try to help!
I would agree with NomDuClavier above - healthcare is a huge one - you want to ensure it will cover you getting to the best place possible ASAP if needed, bear in mind that could well be Singapore rather than the UK but there's certainly a good chance it could be outside Malaysia. Even basic treatments free on the NHS can cost hundreds GBP in Malaysia - my anti-depressant medication was almost impossible to obtain in East Malaysia - would have been in trouble in I hadn't persuaded my UK GP to let me have extra before I left and it was seriously expensive. In contrast the contraceptive pill is available over the counter at £2 per box! Things will probably be more readily available in somewhere like KL than where I am but probably still a good idea to take at least 1-2 months worth of anything you need and ensure you have good health insurance.
I also agree with checking on travel home and communication with home, will you be allowed to use their internet for Skype for example? Will you only be travelling back to the UK with them or do you get flights for your own holiday? What if there is a family emergency and you have to come back to the UK at short notice? Last minute flights are very pricey...
Sounds like you have details of the accommodation but just ensure that you are clear that your room(s) must be air conditioned! Sounds crazy but in the new build houses on our estate all the rooms seem to have air conditioning units except the ones in Amah's quarters!
For clothes, everywhere I have been almost any standard of dress is tolerated but I know that peninsular Malaysia has a higher proportion of Muslims in the population than East Malaysia and you may feel self conscious in a strappy top and tiny shorts out in town - even if it's not actively frowned upon. However, where I live it's not at all uncommon to see ladies in hijab at the mall alongside ladies in hot pants! Definitely something to check as it is extremely hot and sticky here. Many of the work dresses I brought from the UK are awful as even light cotton ones have polyester linings that glue themselves to you. I am going to try getting some new dresses made here as I find it nearly impossible to buy clothes - I am a UK 14 and that is at least an XL anywhere in Asia - then not a stylish fit!
Will your employers allow you time/money for language lessons? You will be able to function fine with English and/or Mandarin but you might find it more enjoyable to be able to shop and socialise if you speak some Malay. I only know a very little but love the positive reaction I get when I try.
You will need a letter from your employer confirming salary to set up bank account, you will also need to show your work visa I think - at least the temporary one. If you go for a global bank you can link UK and Malaysian accounts to reduce the cost of moving money around. You will also need your passport for getting a mobile phone SIM card and your work visa for car finance. Documents in English are generally fine but there may be things I never had to deal with regarding tax and visas - definitely check how that works.
Will your employer provide access to a vehicle? Cars are heavily taxed and massively expensive - 2nd hand cost more than in the UK!
You will need an international drivers permit from the UK - this is acceptable for 1 year and during that time if you are staying longer you need to apply for a Malaysian licence (and / or a state one I think).
I'm sure there is loads I haven't thought of but I hope this helps a bit and doesn't just duplicate too much of what's already posted. Malaysia is an amazing country and I hope you have a great experience!
Salamat Datang Malaysia!