A human can be taught to be like Minato or Jiraiya, with luck. Not like Naruto. I think.

Water makes it easier to form, a leather ball needs much strength to pop, an air balloon will pop if Rasengan isn't stable.

Civilians have bodily chakra they got from Hagoromo. They also have physical and mental energy aka chakra reserves. The trick Madara and many others talk about, however, civilians do not know. And without it, they can't create the type of chakra ninja use (忍術チャクラ).

A half of Kurama is still larger than any human. Naruto became inhumanly good at chakra balancing by the time he learned Sage Mode and Shikamaru treated chakra with unusual composition as something unusual during his fight with Tayuya so this shouldn't be something normal ninja do.

This thing makes me think that both energies have a different function, are real, and are present within every real world object; when, for example, Shikamaru controls shadows, he does it by manipulating their mental/spiritual energy with chakra. Ninja must balance their chakra so that it can be used to produce solid (physical energy) phenomena with a structure (mental energy). Also, Ebisu said that energy comes from food and rest and Kakashi said both energies need to be squeezed out of the body; spirits, unlike brains, don't need to eat and rest.

Food is the source of physical energy. Physical energy feeds your brain. The brain generates, or helps you generate, mental energy. When you extract the energies and mix them together in a perfectly balanced way, ninjutsu chakra is created.

Chakra reserves equal the lowest of your energies though; even if the amount of mental energy you generate suddenly grows, you can't convert it to ninjutsu chakra without a corresponding amount of physical energy. And don't forget that energy comes from food; if everything you eat is converted to mental energy, you might get sick or die.

Lack of connection should be an advantage since you can simply connect everything the way you want. While with an older brain you need a way to merge 2 different brains somehow.

Ninja make chakra through a process called chakra kneading (チャクラを練る) by squeezing physical and mental energy from their bodies and mixing them in a perfectly balanced way, their bodies extracts energy from food. Where do "souls" and "yin chakra" come from?

Physical energy can be used to feed the brain and generate more mental energy, the reverse isn't true so Asura's descendants should have more chakra. Don't forget that to kneed high quality chakra the energies must be mixed in a perfectly balanced way.

Well. I don't feel like wasting hours to confirm something that doesn't make sense and is largely irrelevant.

In Kabuto's backstory, Danzo threatened the orphanage. But had no reason to attack it since he got what he wanted.

This makes no sense. Do you expect me to believe all orphans get an empty apartment and are raised by stealthy ninja they never meet? This is funnier but likely wrong.

No. 4 times Kakashi's. And even that is only thanks to the seal.

Chakra used by ninja is created by extracting physical and mental energy from the body and mixing them together. Chakra given by Hagoromo is only a tool that makes such an operation possible. Anyone who has a lot of stamina can produce a lot of chakra.

Maybe he can, even if we never saw anyone but the true owner do it in the manga. It's kinda pointless when he has infinite energy though.

Can a red eye turn red?

I'm almost certain stolen eyes can't be turned off.