Even i've planned to do ACCA. I had Business Studies, AICT, Accounting and Economics. Economics would be a very useful subject if yer considering MBA. For ACCA, yer Accounting must be upto the mark. AS math is also a requirement fer some universities if yuh want to do BBA.
So do yuh mean that yuh would either do A level economics or economics and math AS level?
And i agree that economics A2 syllabus is extremely lengthy and difficult but everything in life is difficult and i believe yuh'll be able to secure a fine grade.