Meaning of ‘What is left of them’

Meaning of ‘What is left of them’

The passage below is from A History of the Index by Dennis Duncan.

When Cicero, the great Roman statesman and orator, decided to tidy up his personal library, one of the jobs that needed doing was the fixing of these labels to each roll. He writes to his friend Atticus:

It will be delightful of you to pay us a visit. You will find that Tyrannio has made a wonderful job of arranging my books. What is left of them is much better than I expected. And I should be grateful if you would send me a couple of your library clerks to help Tyrannio with the gluing and other operations, and tell them to bring a bit of parchment for the labels, sittybae as I believe you Greeks call them.

I have four questions for the underlined phrase.

First, what does the underlined ‘them’ represent? It seems to refer to ‘my books’. (Am I right?)

Second, what does ‘What is left of them’ mean?

‘What is left of them’ seems to refer to ‘my books’ that’s not finished arranging yet. (Am I right?)

If I am right I’m not happy.

Since ‘What is left of them’ doesn’t seem to fit with the lest of the sentence, that is ‘is much better than I expected’.

Cicero tried to rearrange his library and it doesn’t finish yet, but so far the result was satisfactory. (Am I right?)

Now the underlined part comes up.

My third question.

How is ‘What is left of them’, that is the part of the books that’s not done arranging ‘much better than he expected’?

Last question. Does the underlined ‘gluing’ mean to glue the labels, or something I didn’t understand?

Thanks in advance.