I read your question.
I don't know the other denominations, so I'll explain the Rinzai sect Myoshinji school to which I belong.
There are probably many people who don't know, but when you recite sutras, they are roughly divided into “ritsuju (ritsuju)” and “zaju (zaju),” in other words, whether you recite sutras standing or sitting down.
According to stories I've heard before, manners such as chanting sutras are assumed to be on the roof tiles of the main temple or Buddha hall (I think it would be easy to understand if you could imagine a hall with a cloud dragon on the ceiling of a famous temple in Kyoto), so it seems that recitation is official. Therefore, I don't think there are any specific regulations regarding sitting and reciting, but 90 percent of people are seated upright. I rarely see people zazen, but I've only seen people zazen meditating for reasons such as knee pain.
I hadn't even thought about breathing, but I take a few breaths while reciting sutras. It's unprofessional, so I don't know if it's right, but if you take a breath, it's probably because you're not breathing. Swimming is like that, isn't it?
Conversely, at least I can't recite sutras while breathing.
In Japan, we often enter from a mold, as is called a “culture of forms,” and of course I think that is important, but there are many things that you don't understand until you try cooking food. Besides, “Oh do it, do it this way.” I've seen a lot of people who are confused because they have been taught too much.
It's made for relaxation, so why not do it without making too many rules? There will also be things you will notice within yourself, so I think it would be nice if we made improvements at that time.