You're welcome (and thanks, since that website is mine).
a) Never copypaste from Word into the Visual editor: Word isn't designed for that purpose, and it introduces wrong code that messes things up. If you copypaste, paste into the Text editor, so that only the text will be pasted, then continue formatting via the tools of the Visual editor or via coding.
b) The problem with the h3 headings in the post you linked to has to do with the theme you're using: in many themes headings have a default bottom margin but in The Columnist they don't. Plus, because of Word, each h3 is enclosed in (totally superfluous) div tags: plain divs are always 'neutral' (no margins etc unless you specify otherwise). So first you need to remove all these from around each h3:
One way to add margin below each h3 heading is to turn these:
(You can change the number, of course, to adjust the amount of blank space.)
But since you have the Custom Design upgrade, you can change the headings once for all in the CSS editor instead of modifying each separate heading in the post editor (assuming you do want uniform headings throughout your posts).
You probably need to improve some things in your CSS anyway: the original CSS of the theme specifies bold text for headings, you've cancelled that and turned them to italics via CSS editing, and now you're turning them back to bold in the post and trying to italicise the book titles.