For my hand quilting classes I use the "No Slip Hoop". It is 14" and available from JoAnn's and other stores. It is constructed in a way that when you get the quilt fixed it doesn't slip or move. I find the 14" is large enough for large quilts.
Also for practice you might try 1/8" gingham check fabric. This will give you lines and spaces to practice your stitches. And......remember it is the evenness of the stitch and not the size that is important. Smaller stitches come with practice. Also, don't obsess with trying to make the back stitches the same as the top. Work for good penetration of the quilt so that all stitches come to the back. This also comes with practice.