I know the answer to the H. It's kind of funny - and supposedly true.
Mark Twain worked as a typesetter back in the day. He was given a sermon from an out of town minister to type set and print. After spending a couple of hours laying out the text with those little lead letter pieces, he got to the very end. The last two words were Jesus Christ - BUT, there wasn't enough room on the page to fit it. That meant he either had to re-typeset the enter thing or print an addition page for just the name. His solution was to use the abbreviation of J.C. - it fit perfectly.
The minister freaked when he saw it and demanded that the entire bundle be reprinted using the "full name" of the Son of God. Mark Twain was irritated at having his boss mad at him and that the minister was being difficult. So, he re typeset the entire thing and when he got to the very end, he added the initial "H" as a joke making Jesus H. Christ. He was blaspheming according to the minister and his boss and lost his job. He wrote it in to one of his short stories where it now lives on as a exclamation.
p.s. I did a term paper on Mark Twain in High School.