personally kind of wish they'd have new signers in the series as there's only so many times you can see a daniel radcliffe auto and get excited over it.. never thought I'd say that when I like the harry potter movies.. *LOL*
The problem with the HP series is that there are very few cast changes with each new movie. It's obvious that Artbox has had problems getting autos for Hagrid, Snape, Mr. and Mrs. Weasley, and Dobby. Otherwise, we would have seen those cards in other sets. We haven't even seen costumes for Snape and the Weasley parents. A Snape costume would be the one time I wouldn't complain about getting another all-black swatch!
With the supply of main character autos exhausted, Artbox
did get new signers, six of them: Griphook, Young James Potter, Auror Dawlish, Karkaroff's Aide, Professor Grubbly-Plank, and Slightly Creepy Boy. IMHO, all but Slightly Creepy Boy are legitimate autos (although a case could be made that Young James Potter isn't a legitimate auto, either, as he had less screen time than Slightly Creepy Boy due to that sequence about Snape's memory being drastically cut from what had been filmed).
The other thing is that for those of us who can't afford or haven't been lucky enough to pull a Harry auto, the inclusion of that auto in this set
is exciting. It's one more chance people will have to pick up the most important auto in the set. When you combine it in a dual auto with Sirius, well, be still my heart.

Sadly, it's yet another card that I will never own.
And how many boxes per case should have only one insert this time?
Four boxes in each 10-box case will have only one insert. Again, IMHO, this is one of those times when I think people would be better off buying an entire case than buying a couple of boxes.