I have had many quilted bags and am making several right now for selling for my new sewing machine and I do not believe that you need to do anything extra to reinforce the seams to hold up. I always sew the handles an extra backstitch or two just because they hold the weight of the bag pulling down. I also believe if you add (I use plastic canvas, some use cardboard, foam board, mat board, etc.) a bottom type sewn envelope will help with structure.
These are beautiful bags and I love the color choices you have choosen. Best of luck!!