Balance: It's all based on physics, but it can refer to many different things. In order to have balance, one must be coordinated and be able to have good control over their body. Body mass, weight etc all ties into having balance, but again, it comes down to coordination. Gravity is very important when one talks about balance.
Momentum: It is the mass and velocity of an object. How fast an object is moving. Momentum can increase based on setting or the object that's being moved. For example, if someone throws a ball down a slope (hill), the momentum of the ball will increase because of the setting. It will pick up on speed because gravity will pull it towards the ground (bottom of hill).
Capacity: It is the total amount of something that can be produced or contain. For example, all water bottles have a certain capacity of water it can hold. Also Area and Volumn tie into capacity.
Flow: Flow is kinda confusing for me because everyone have their own opinion. Flow can be unintendid and just happens on its own. Gravity/Setting ties into flow becuase it alters how flow of something may be moved. Such as water flowing down a stream.
Taijutsu: Taijutsu is a style of fighting. It is using your physical and mental strength to fight. You have to have good stamina and endurance and it's a hand to hand combat because you are in contact with the enemy most of the time, even though some tai maybe be at different range. Tai is not like Nin or Gen, it doesn't require chakra. Even though certain taijutsu moves may involve the use of chakra. Like you said, flow, momentum, capacity and balance also ties into it. Gravity is a major factor in Tai.
