Yeah, 3 options: medium format glass carrier, full frame carrier, or filed out carrier. For example, for a Beseler 23C, look for the 8072 (glass), 8055 (full frame), or 8053's and file them out. The 8055 is 25x37 mm, the 8053 is smaller. The 8055 will give you black borders and a little bit of sprocket hole and a smoother edge. You can mask it down further with your easel if you want just an even black line around your print.
If you want the ragged edge sloppy look, get a second normal carrier and file it down. Paint the filed edges black (or use a sharpie) unless you want that black-white-black border effect (like the first link in this
thread. That comes from reflections off the silvered edge.
If you want the whole negative, or two, you need a medium format sized carrier. I did this print with the glass carrier mentioned above:
If you do buy a glass carrier, you can go with the cheaper non-anti-newton glass one, and purchase new anti-newton glass from a place like Focal Point for about $20. It might save you money.
You could also make one out of matt board or foam core like you said, but it won't necessarily have all of the properties of the above options. It will be cheaper though. Actually, Beseler carriers can be had for $5 now if you look, so not all that much cheaper.
As to the non-cropped images on paper, I just leave white boarders around the edges. Makes it easier to mount and easier to handle too.
