Kongo is a wonderful T5 BB when used right! Her main gun range can make a tier 7 or 8 blush but her accuracy at those range are not that great though you can occasionally get some devastating strike on it. Kongo excels in mid range combat and if you're good, even close range! I usually lead attacks and be around 10km - 15km away from enemies, if I see an opportunity to push, engagement will be close as 5km. Use her manuverability and speed to your advantage, she can get in and out of situations easily.
When engaging other battleships, come in at an angle, Kongo's broadside isn't as thick as the others (for speed of course!). Your speed will be at an advantage when engaging another Battleship, you either can get close and circle them or get out of their range (while wiggling).