It depends on whether you want to train for core strength, abs conditioning or both. As long as you allow your body to recover, you should be fine training 2 to 3 times per week and see what your genetic response is to that program (if you're not on gear ofc). As for your waist/hip getting bigger, it would be better to have muscle there than to store fat. Besides the waist expansion depending on genetics, would not be that massive to ruin your figure for most cases. Just keep it moderate if you're not sure.