I take politics, history, economics and philosophy - so maxing out on the essays.
If I were you I would want to do another essay subject, I'm starting A2 next year (just done AS) and I can tell you that economics isn't really an essay writing subject in that the quality and coherency of what's written does not matter.
That said economics does help a lot with history, in fact all modern history is tied with economics, and so for example whereas other A level students just learn that Mrs Thatcher's adopted supply side polices from the textbook, you will actually know what that means.
If you want to do history then I don't see why you are taking 2 sciences, my advice is take Eng lit, geography or politics; essentially any respected humanity. That isn't to say don't take any sciences, just not 2. Also I would advise you rather than science to take maths unless you hate it, as whatever you do after uni this will definitely help you (employability wise).
In regards to languages I am not aware of any massive advantage possessed by students who take this, most history A level students do not.
In regards to GCSEs, they do not matter unless you are going for Oxbridge. I know that's pretty crushing having just spent 2 months revising for them but the thing is unless you do really badly top unis (save Oxbridge) don't care. I did reasonably well acquiring 7A* and 3As, but I really dn't think that will give me the edge over someone who only got say 4A*s.