If you’ve made up your mind to complete both the qualifications, the most optimum way forward would be this: Begin with CA and complete up to the IPCC examinations.You will have approximately 2 years of work experience (articleship) before you begin studying full-time for Final CA.
This will entitle you to 5 papers (6 if you are also a graduate) of ACCA. In this time frame, you start studying for ACCA. F5 and F9 can be completed relatively quickly as the syllabus overlaps with the IPCC examinations of Costing and FM. Study F7, P1, P2, P3 with diligence in the following year along with articleship. Opt for either P4, P5, P7 as your final 2 papers, as this overlaps with your Final CA syllabus. Like a symbiotic relationship, completing IPCC will ease your effort for the Fundamental level of ACCA, and the Professional level of ACCA will ease your effort for a few subjects for Final CA. Attempt your Final CA. 3 years of work experience can be counted towards both the qualifications. This would allow you to complete CA as well as ACCA in the same time frame it would take for CA (notice how you begin with CA and end with CA without flexing the timeline, and complete ACCA in the interim). It would be a great combination, but not a necessary one. It is useful for the following reasons: You would like an international qualification along with CA and enhance your CV. You plan to find work overseas in the field of finance. You are particularly aiming to secure a job which requires a CA+ACCA (lots of companies adopting or consulting for IFRS are looking for such candidates). Apart from the above, it would be slightly redundant to pursue both qualifications as CA and ACCA by themselves are sufficient.
Check out few other links on ACCA and CA.