I was born in Sydney & moved to the UK 17yrs ago. I return to Aus on a regular basis including time in Adelaide, but have also travelled around Aus. Adelaide is like a large country town, rather than a huge high rise, high paced city. I too live in London, and even Sydney now feels much slower when I return. Adelaide, is even slower than that, but it only takes a few days/weeks to slow down.
I agree with others that Adelaide is great for food & friendly family life. Not the place I'd go if single or was trying to find work in say a larger international company. Once settled, I'd recommend trying to see other places, but remember, that Aus us as large as Europe and takes 5hrs to FLY across the continent! Western Aus is also very laid back and very spread out with many hidden treasures not so well known abroad. The East coast is very touristy, more built up and far more expensive, but better know touristy things to see.
There is a thing called 'Tall Poppy Syndrome'. Australians will generally downplay their job, title, pay rate etc and discredit those than boast about their own credentials. There isn't the same class system as in the UK.
Unlike the UK where you might have a different accent from only living a few miles away, this isn't the case in Aus. I might be able to say that someone lived in a more rural area than a city, but I'd never say, 'Oh, that's a Perth accent or a Cairns accent'. South Australian have a few words that are pronounced slightly different, but the distinction between the whole country is very small. The terms for certain things, such as the size of beers differs from each state though.
Brits make up the largest immigrants, so there are multiple British groups/ex-pat groups you could join to meet new people. The lifestyle is more laid back than I find in London. Due to the heat and being laid back, people don't get as dressed up as one might in the UK for a similar event. Due to the proximity to Sth East Asian, there tends to be more Thai/Chinese and Vietnamese influence in food in some cases. I'd never tried a great Indian meal till in London, but can't comment about Adelaide specifically for this.
Watch youtube videos of 'Wanted Down under'. Obviously the Adelaide episodes. Like any place, there can be a vast difference between living in the city centre, rural, beachside or in the hills. This will obviously depend on where your DH needs to work and how long the commute might be.
Where possible, rent out your home back in the UK. It will give you the option to move back after the job finishes, OR, sell up and buy in Aus if that ends up being the plan. Best of luck, but think of it as a fantastic opportunity. I lived abroad in the middle east ages 8-11. I'm sure my parents were sceptical, but for me, it was amazing. I still remember our travels and experience and it opened my eyes to different cultures and experiences I would never have had otherwise. Enjoy 