I don't bother with putting the grain line on the outside, I arrange the triangles in the pattern I like best. But I am very careful NOT to stretch the bias edges, and have not had any problems. I don't starch, because you aren't supposed to prewash your fabric, but if you are really worried that you'll stretch the edges (and no matter how you arrange them, there are still bias edges) go ahead and add some extra starch. Good luck!
P.S. Maxine does say in the book that you can arrange your tri's any way you want.