A: Let's figure out how to make it work for any size cards! I'll add these instructions and measurements for A2 and 5" x 5" cards to the tutorial page.
For the piece in Step 1 of the tutorial, the width will be the width of your cards plus 1/4". The length of this piece will be 2 times the height of your card plus 1 1/2" (that adds 1" for the bottom and 1/4" of height to each side of the tote). Score at [card height plus 1/4"] from each end.
The length of the piece in Step 5 will be the same as the perimeter of the bottom of the tote, 2 times the width plus 2". Subtract 1" from the score measurement above for the width of this piece.
Make the first score line at 1/2 the width of the tote, the next line 1" over, the next line the full width of the tote, then again 1" over.

A: Thanks for the reminder that I need new plates! When the cut lines start to leave marks on the cardstock, you can lay a sheet of text weight or parchment paper between the die and top plate. When you get new plates keep the top one free from cuts, and face the cutting side of the dies down into the lower plate. I cut into a metal plate, but a self-healing mat might be a good option for you as well.

A: That sounds like the Triple Stamping technique. You can also do the stamping and/or coloring first on a single panel, then die cut with nesting dies and layer the pieces back together with narrow mats - the finished effect would be the same.

A: Hot press watercolor paper is best suited for stamping because it has a smooth finish (think of an iron as a literal hot press, smoothing wrinkles). Quality and results will vary depending on the brand of paper as well as the cotton content. Don't start off with cheap paper just because you are a beginner - you will only be frustrated with the results! I use Fabriano Studio hot press paper for my cardmaking, in the 140# weight. I buy the biggest pad of 11" x 14" paper which is 75 sheets - I can make 450 card fronts from that amount (from the long side, cut at 4 1/4" and 8 1/2", and cut those strips in half to make four A2 panels. The remaining strip is 5 1/2" wide, and you can cut it into two square panels, or cut two A2 panels and have a little extra piece for sentiments. Inks: for watercoloring I use Versafine Clair or a hybrid ink - anything that doesn't react with water will be fine.

A: I have used hybrid inks on fabric - they are waterproof and dry quickly (the ones I have are from Impression Obsession; many of the small company branded inks have the same formula). Versacraft ink by Tsukineko can also be heat set for permanence on fabric (it was originally called Fabrico ink). Stazon and archival inks should work too. You might also look into a product called Terial Magic Fabric Spray - it is sprayed onto fabric to stiffen it like paper, and it washes out after you've done your printing or stitching.