You can use the 6x7 carrier, you can just mask the opening down to 645 using construction paper. Have the opening in the center of the 6x7 not to one side of the other. And yes you can make carriers out of cardboard, I perfer black core mat board or illustration board. You can also make your own easel with heavy mat board. I have a whole series for for 11x14, 8x10, 5x7 paper with varying border widths. Just the other night I made one for a full frame 35mm with a thin black line around the 4x6 image on 5x7 paper, took about 30 minutes. You do need a good timer, a Gralab 300 or Timeolight will work just fine but for better control an electronic timer with .10 sec increments would be better. As for lenses, the inexpensive lenses will be "ok" for 5x7's or 8x10's with minimum cropping, but for the best quality go with a high grade lens from Nikon, Rodenstock, Schneider. You will find everything you need on the Bay or the "list", it just takes some time to find it all.