Looking for advice on possible subject combination for Econ / Finance

I am thinking of taking Further Math, Economics and Accounting (4) A-Levels, with the hope of getting into LSE, UCL, or Oxford. Will taking a 4th Subject (Accounting) be advantageous if I get all at A*/A?

You've only listed three subjects ("Further Math, Economics and Accounting"), yet are asking about the value of taking four, with the fourth being Accounting. That doesn't bode well.

Wouldn't Further maths be considered as 2 subjects at A level?

I am thinking of taking Further Math, Economics and Accounting (4) A-Levels, with the hope of getting into LSE, UCL, or Oxford. Will taking a 4th Subject (Accounting) be advantageous if I get all at A*/A?

Assuming you're meaning you're thinking of taking maths, FM, economics and accounting as the a-levels (rather than not mentioning maths?), a fourth isn't super useful. But if you are going to do a 4th, then accounting probably isn't the best idea, some of the top unis look down on candidates doing business/accounting when they're already doing a-level economics as they're either seen as too similar or not academic subjects (rather vocational ones). If you check on some of their entry requirements, some like LSE state they would like a fourth subject to ideally be an essay subject if you're already doing maths and further maths, so stuff like history, politics, etc.

So do I think you can get into top unis with accounting as a fourth a-level given good grades in all subjects, sure. Is it the ideal subject combinations, probably not. Will it limit your chances, difficult to say as only the admissions teams know this rather than people on TSR. Is it more important to get good grades in 3 a-levels than do slightly worse in 4, yes.

I see. So would it be better to take Maths, Economics, Literature as my 3, for LSE economics per say?

No, for LSE you have to take maths and further maths as a minimum. Maths, FM, Econ is fine for three but if 4th then I'd either do a science like physics or an essay humanity/social science, but there's no strict rule on the 4th