Oh bummer
If all three photos were Smart Objects (that is, if you'd used File>Place to put them in the design) you could have simply increased the resolution of the design and you wouldn't have needed to redo anything. Alas, you haven't done that.
PLEASE read over that section of the Layers & Masks Class again.
Oh gosh, yeah, that's MUCH too low resolution.
Generally, print resolution is 300 pixels per inch. However, you should speak to the printer to confirm that - some of them differ.
Also, this is very important information.
I have seen the Lens Corrections to do some pretty awful things to photos when left on all the time. Distortion and stuff. As Sam said, use them as needed.
Camera Raw Default is how a photo looks before you begin editing it.
Since CRD fixed this problem, it means that the problem was caused by something you did editing.
Great! So go ahead and do your raw processing again, and watch out for it.
By the way, I beg you to consider a refresher of The Raw Class. The new updated material will blow you away. As a previous member, the price is significantly discounted.
Oh, sorry, I see what you mean!
Yes, if you don't wish to buy a suitable overlay to use, you really would make one with sandpaper, I reckon. Probably paint black paint onto white paper, then scuff it artistically.
I'm flummoxed, sorry. I have no idea what it would be.
I assume that if you choose "Camera Raw Defaults" from the little submenu over on the right-hand side, it's still there?