in your first year's prelims you can get away with writing just 7 essays (out of 12). If you're good with maths / abstract stuff, doing 2 Maths questions for economics, and 3 logic questions for philosophy, should ease your workload by quite a lot. If you don't like maths / logic, then you can also get away with doing 11 essays, there's just the one (very easy) compulsory maths question for economics.