1. Heat n Bond is stiff. Normally, if you plan to use 100% quilting cotton, I'd suggest Mistyfuse, but since you're only doing a zig-zag stitch, having a stronger bond between the fabrics would be more desirable. What fusible is used doesn't matter much for a wall quilt & to wash applique that has a raw edge & is only held on with a standard length zigzag requires a heavier fusible.
2. I wouldn't leave just a border if you plan to wash it a lot & use a zigzag (unless "zigzag" is code for stitching it close together multiple times around, creating a faux satin stitch -- in which case I would definitely window, leaving 1/2" around inner edge & would at least switch to Pellon 805)
3. Echo quilting usually looks nice & it will draw more attention to the words. It would be easier to make recommendations if we could see the fabrics & layout.