I always let the carbon prints and Print Shield dry overnight. One huge advantage of the solvent based Print Shield is that it is not tacky. The water based coatings are, in my opinion, a disaster in that respect. I tried them for a while and had apparently dry prints stick to each other.
For interleaving, if I use any, it's usually just modern typing paper. The type I get at Costco is buffered. (An acid test pen is useful to have around.) Most modern typing paper appears to be buffered, probably because the government established standards for document longevity that all seem to follow. Note that I'm not a trained, museum archivist; so this info is a distillation of what I've retained from my reading on the subject for my own purposes. There is a Yahoo "photoconservation" forum that has the real experts on it. See
<photoconservation@yahoogroups.com>. I am a passive member of that group.
The thing I guard against most in mailing is bending and abrasion. So, I sandwich prints between cardboard (the usual box corrugated -- and acidic -- type) that is tightly taped together, then put into a stiff USPS envelope, with smooth (buffered) typing paper protecting the face of the print -- from both abrasion and the acidic cardboard. I believe the Post Office will stamp "Do Not Bend" (or the like) on the envelope. I've never had a problem with this approach. Needless to say, don't store prints with this cardboard. It's only for very short term mailing protection, and buffered typing paper is between the cardboard and print.
As a side note, my old 8x10 inch silver print proofs, which are well processed, are stored in a metal file cabinet in my darkroom. (Yes, I still have one -- now often referred to as the ink mixing room.) The back of the prints show the effects of air-borne acids yellowing from the edges in. It's probably the file folders that are the source of the acids. Library research showed that old books stored in sealed containers yellowed at 10 times the rate of those that were open to the air. Most acids will actually float away in the air if they can. Sealing prints with acidic papers is the problem. Acids travel through the air (on water molecules); buffers do not migrate. Some old book storage practices include having buffered sheets periodically in the pages of the old book. The acids don't attack the cellulose fibers immediately at every contact. On the other hand, buffers do grab the acidic molecules immediately when they make contact. So, buffered sheets in the same container with prints do help minimize the airborne acids.
For long term storage, beware of cheap boxes. They are not acid free, and, as noted, acids migrate through the air.
https://www.archivalmethods.com/ has lots of different acid free boxes. And if you're as cheap as I am, you can also use aluminum foil to totally line the inside of the box and lid. Acids can't get through the foil. Then have buffered paper at the top and bottom of the stack in the box. Of course, being a Californian who has lived with brush fires forever, the real trick is to have a couple external drives in bank boxes, along with the old film negatives. When the fire wipes out the archival boxes in the home, we can always reprint our best images. (One of my local banks got flooded, so I insist on a box that is well off the floor.)
Nothing is forever, but it's nice to think that our best prints might last for hundreds of years. Most people I know enjoy the old family photos from the distant past, though few seem to keep any of the other types of photos. That said, I and our retired local art museum curator (also of the Boston Museum of Art), have paintings from our old relatives/mentors above our dressers.
Paul