You should definitely keep Gothitelle on your team. I assume you have Pokemon Black? (Since Gothitelle is version-exclusive, you can get it on Black only). In terms of gym battles, I would suggest you to choose Snivy as your starter. Catch a Pidove, and a ground-type because they will be pretty useful. You can also experiment with electric types as well, a good suggestion would be Blitzle and Emolga.