Mr. Capp,
The newer paper just needs to be as flat as possible when it goes in the machine, so I don't wet the back, and yes, I use the sheet feeder. First, if you look at the sheet after you have flattened it, one side still has a little bit of a curl compared to the other. At least that's my experience. Turn the paper so that side is to the left as you face the machine. That means when the print head goes over the edge, it's the flattest of the two edges, so you won't likely get head strikes. As you look down into the slot, make sure the paper is at the bottom and flat as possible all the way across when it feeds. You will have to get it positioned as best you can, reach over and hit the feed button once, and get your fingers back in there behind the plastic curved guides and push downwards and back with the back of your fingernails. The machine will make some noise, and then, suddenly, it will grab the paper. It will scare you. Just don't get your fingers too far down in there. You'll reflexively pull them out as soon as it grabs the paper.
Look at the edges and see if they look straight and approximately centered compared to the edges of the guides, which have now retracted away from the paper edges. It's never perfectly centered, but it should look perfectly straight. The machine will do an up and down motion with the paper when it's in the print position, so it's kind of testing whether it is straight, too. Then it will stop and the display will say "ready." The centering on mine seems to leave a little more gap on the left than the right, so I dial in a little more space on the right of the image to get the image accurately centered on the paper. You'll have to experiment to determine how much extra space to give it.
As far as mounting is concerned, I've been using corners with the 17"x25" and getting good results, but I'm about to experiment with some new dry mount tissue that is made for low temperature mounting of inkjet images.
Aloha, Aaron