Im wondering what are the best books for developing ki, explaining and showing exercises, breathing methods and meditation? and explaining what it is for.
How would these books compare to:
Ki in Daily Life
Book of Ki
by Koichi Tohei
Also, I know this is a silly question but, what are the differences between the breathing exercises and meditations for aikido/ki and zen?
I doubt that it's the best book on the subject, but I wrote one:
It's a manual with very basic exercises for how to start one's ki flow, and get it going - not only for aikido practitioners.
Koichi Tohei's books are excellent and very trustworthy, so don't expect to find books that surpass them. But it's always good to get different points of view.
For the very source of it all, check the Yellow Emperor, the Chinese classic that most health and energy traditions of the East are based on.
There are many different methods of meditation. Aikido students usually meditate quite zen-like, when they do it at all. Then there are all kinds of Indian ways, et cetera, et cetera.
As for breathing exercises, they are traditionally focused on the ki flow, whether they are aikido, zen, or Indian (where ki is called prana).
When you dig deep into a life energy tradition - wherever it originates - it tends to be very complex and particular. But the basics of it has many similarities in most traditions.
You can use whatever method, but be persistent and patient. Breathing takes time to reform, and more time to transform.