Any discipline or stream in graduation is good for anyone, as the UPSC Civil Services Exam considers the particular subjects in which a candidate has done his/her graduation. So you are eligible. More than that however, it depends on the subjects you choose in BA and if they are of your interest. Therefore, pls start preparing for Civil Services exam and continue your BA.
All the best!
Yes, BA is very beneficial if you want to prepare for IAS while graduation. Through BA you already have a grasp on general studies and most of the subject realted to UPSC syllabus. BA is the plus point for improved GS and Optional subjects. Also, BA is generally easier as compared to any other option so its less time consuming and you can focus on the preparations.
All The Best.