Regarding Kok, well if it is a female you wont be able to get a big kok out of her, eventhought some females develop nice koks too we only could know with proper carings of your fish so stick to what the link of above says.
the best food and clean water. kok's are gentic so if his mom and dad didnt have a big kok the likly he wont eather. but they best thing u can do is clean water and good food. as well verity of foods too.