I think having about 7 outfits to start off with is ideal. You want options and don't want to be washing things out every evening.
Have a look at next and gap for great basics and then splash out on a couple of things you love like a great scarf or bag. Luckiy for you the sales are on so you should get more for your money.
In terms of items I'd start off with:
Cigarette or narrow cut trousers in black or grey. Next have some great cotton cigarette pants for £28 I have a pair and they have been brilliant
Pencil skirts- gap have great ones also Zara have some great ones in a number of colours (black, green, blue, red etc) for under £30
White or neutral coloured shirt. I don't suit white so go for cream or peach with are better with my colouring
Couple of jersey tops in your favourite colours. Try Boden.
Cardigan. I think people spilt into twin set style cardigan lovers, nipped in with a belt or grandad style ie longer. Personally I wear twinsets style cardigans nipped in with a belt and a pencil skirt loads. But I have seen others rock the longer grandad style too.
Couple of dresses. Try Boden or great plains. I love wrap dresses as I can tie them to fit my figure.
If you like jackets try top shop or uniglo or Zara.
Then it's over to belts, shoes, scarves, bags and jewellery which you can use to dress up/ change an outfit.
What a obout coats? I'd recommend a good Trench coat- M&S, banana republic, gap etc
I will do some links in a mo
Very best of luck with your new job!