If you are going to be directly employed by Aramco, then accommodation will most likely be in Dhahran. I would assume that there is company provided transport from Dhahran camp to Dammam. You do not strictly need a car, but after a month or 2 you will tire of buses and having to arrange your life around them.
Badics will be in the house - welcome pack of bread, pasta, tea, coffee etc to get you through the first night. Refridgerator and dishwasher should be supplied, but washer and dryer either you rent from Aramco for a short time or buy. Basic furnishings will be provided also from Aramco warehouse but they are basic and you will want to replace them asap.
You could ship furniture etc. across but the shipping allowance is more than enough to furnish the house to an acceptable standard.
Electrics - in the house likely will be mostly 120V, but you will have a few 230v uk style sockets in kitchen living room, bedroom perhaps. Most electronics work fine on both voltages, just buy some 120v plugs from the souq and change them. Kitchen appliances I would buy here as you feel the need for them.
SIM card you can get at the airport, buy a prepay package for calls and data to keep you going until your IQAMA is processed. As soon as you have Iqama you can apply for a driving licence and have 2 mobile sim - I use 1 for calls and data and a 2nd for a 4g router for the house.
Forget about using a UK phone - £1 per minute to receive, 30p per text to send makes it extortionate. You can use messenger, facetime, skype, whatsapp etc to call. I keep a UK sim in a dual sim phone and basically send 1 text every month to keep the SIM active.
Youl get most things you are used to in the commissary at a slight premium, but there seems to have been a dearth of IRN BRU recently. I have about 30 cans left that were in stock last month (full fat) that I am slowly working my way through.
Dress code in the workplace is a delight compared to the UK. Smart casual - trousers, shirt and shoes. Bring a light jacket with you - winter can get as cold as 8c in the mornings, and on the odd occasion when it rains it chucks it down.