Hi Paul,
At this point, don't worry about deleting your old posts. -you already put Closed in the title, so people shouldn't care about those anymore.
The way to make one thread with all your books in it is actually very easy. You seem to know how to create a thread, and have a listing with all the important info in it, so you're more than halfway there.
Start a new thread, give it the title you want, and post your rules for the sales thread, returns accepted or not, shipping fees, and that brief introduction to yourself. Do all of that and then hit submit.
Next, on your second post in this thread, you can show which book you're selling, its price, and the picture or scan provided.
Then, in your third post, you can list your second book that you're selling. Show the price and a picture again.
And so, it's pretty easy. Just use a new post, within your sales thread, for each book that you want to try to sell.
You only need to list your rules in the very first post.
Good luck!
Andy