Salam Alaikum
I've been out here for 2 1/2 years now.
I'm based in the Dharahn area so I'm on the other side of the country from Jeddah.
Jeddah is a bit more conservative as it's closer to Mekkah, but it's up in the mountains so the weather is better.
You will get private medical (compulsory for your employer to provide it)
You should get accommodation as well. Probably on a compound.
Compound life is like a small village really, at least mine is.
It really depends on who you are working for.
Some companies have their own compounds, others just rent a few villas in one.
Tax is tricky, as you need to be out of the UK for 12 months or you can be liable for tax, I'm on NT (no tax status so I don't pay tax or NI any more) some companies will pay your tax for you.
You will need a Visa to get in and another to get out of the country, your employer will probably keep your passport while you're in kingdom. You will get an ID card called an Iqama, which you need to carry.
you can get a Multi entry/exit visa which is good for 6 months unlimited entry/exit (I get these as I live very close to Bahrain)
The cost of living can be quite low. Before Katy came out here I could feed myself well for £200 a month, including eating out at least once a week.
You can get 1/2 chicken and a bag of rice (which will probably do for a couple of meals) from a takeaway for £2, 2l of milk 50p, Petrol is 10p/l
The standard of driving out here is awful.
Every day it's like an episode of "Police, Camera, Action"
You get used to it though.
I enjoy it.
There are a few issues,
No pork products.
No cinemas
No Alcohol (barring homebrew which ranges from bad to really bad, most western compounds will have someone making it)
Working with the locals can be a challenge, they don't have a work ethic to speak of. you'll hear the phrase "Tomorrow Insh'allah" quite a lot.
If you can relax and just go with the flow things get a lot easier.
If you have anything else specific PM me and If I don't know, I'll ask about.