I did not understand this

Can you paraphrase /simplify this to me?

"He opens his book recounting his experiences by explaining that since he wanted to write his memoir, having a bunch of time "on his hands" was such a Good Thing that he "could not wait to go to jail!"

my question, I cannot see two different sentences are bound together.
What does "since" refere to here?

secondly why is "Good Thing" written with capital letters?

thanks in advance.