That's a really awesome quilt! Have you seen the pattern in a smaller size? I think I'd probably just add more blocks/rows to the boston common sections to get to the width/length you want and then border as desired. As to yardage...I always over buy. Boo boos, you know. It's about the only way I have any 'stash'. I don't buy something just because I like it. I only buy for projects. You should be able to get a pattern for the lonestar with yardage requirements; same for the boston common blocks. Go from the 54" for the lonestar that was mentioned earlier, add the boston common blocks to see what your quilt width would be and multiply. Add a couple of extra yards for each element and you should be okay.