Interesting! Is this book approachable by someone who knows nothing regarding biology/medicine/etc ? Thanks

Very much so. It's written for an interested and intelligent general audience.

How do you learn to work with the breath?

"The mind illuminated" is a very good introduction to meditation. It is unique in the formal system he used to make sense of the various levels of practice. Very practical and low-BS.

Happened to me before so I can really feel your frustration. What I have learned, because it's not always easy to ask for 50% upfront, is to split the project into many phases and ask for payment when a phase is implemented. Hope you won't have to deal with a client like that in the future.

// If your build is gonna take a minute ...

Same applies if you read a tutorial post while you wait your build to finish ?

I would say yes.

Is it possible to have a similar deal again since from the comments seems there are a lot of developers interesting in your service ? Thanks!