I use an Easy Touch Bar Sander with either 150, or 220 stuck to it to sand my Depron. The Depron sands really well. There are tons of different ways to hinge a Depron plane. Some guys use floppy diskette hinges, some use mini hinge-points...etc.
I have used just about every method that I have seen, but the one I use most often is just a good clear packing tape. The hinges on my Yak were done with packing tape, and the plane has lasted over 6 or 7 months without a single hinge failing. Some folks don't have good luck with taped hinges, and therefore think they are weak, but they work fine for me. I suppose it is all in the application, or technique.
The current, most popular method right now is probably the floppy diskette hinges. Just sand a double bevel on the surfaces like we do the balsa planes, and use the FD material to make small hinges, much like CA hinges. You can either use foam safe CA, epoxy, or just about any other glue that you use on foam.
I think that lots of folks are getting too fancy with these foam planes, and making things FAR too complicated with new fangled techniques, and forgetting why we started building them in the first place. And that was to take a 5 dollar chunk of foam, a few bits of scrap wood, some tape, and turn it into a plane that flies well, and that we can have hours of fun with, without any of the worry involved with destroying the plane. If you totally trash the plane, you can have another one flying that same evening, once you get your building steps in order.
Just my thoughts on the matter, nothing more.
If you need any diagrams of my methods, I can send you some.
Have fun with it !! And remember, with these foamies, there is no right, or wrong way. Just experiment, and have fun !