Thank you everyone for your helpful and detailed responses!
I've revised my budget as follows and it now looks like this:
Rent - $3,500.00
Car Lease / Insurance - $1,800.00
Nursery / Playgroup - $1,000.00
Petrol / Parking / Toll Charges - $600.00 (would be mainly for business travel out west, parking in industrial areas rather than CBD)
Holidays / Short Breaks - $500.00 (put aside each month)
Maid - $300.00 (not required to live in, unless my wife and I were both working)
Groceries - $1,250.00
Socialising - $400.00
Annual return home airfares - $350.00 (put aside each month)
Gas, Water, Electricity - $500.00 (budgeted on the high side and would try to reduce this by minimising air-con use)
Eating Out - $400.00
Clothing / Classes / General Goods for Little One - $400.00
Cable TV - $60.00
Home Contents Insurance - $50.00
Internet / Phone / TV - $50.00
Mortgage / Life Assurance - $40.00
Mobile Phone for Other Half - $50.00
On the car front, it was discussed previously, and they want to play no part in leasing of cars but instead build the expected cost into the basic salary. Working location will be Tuas, and customer visits will be frequent.
For freight, they offered to pay $1k towards it, and this should hopefully cover the basics, bearing in mind that all furniture etc. will remain at home in Scotland.
2 months accommodation is now 1 month's accommodation with one-off costs for white goods etc.
A separate schooling allowance is a non-starter. We will have to take the costs for this and plan accordingly. However, an additional $8k has now been added to the salary to offset some of this.
In terms of where to live, I agree with the suggestions made. A big focus will be on the best place for the whole family, with transport and local facilities / amenities high on the list. The range of options is quite daunting, and we'll look into this in further detail if it all becomes official and the move is definitely going ahead.
All-in-all, definitely keen on the move, but going to spend the next couple of days reviewing the pro's and con's and decide from there. The biggest factors are going to be giving up two good jobs to, at least initially, take one job; and also leaving family and friends behind.