I'd go for a slight (like 1/16" of an inch) overlap, my experience has been when butting up, it always goes slightly offcourse
That is what I would do. As the vinyl shrinks you may see the gap, but it should take a while. I would practice with old vinyl before using this method if you have never done this before.ive been in the vinyl biz on and off for a while. if this was my project, i would think about this option:
overlap a little bit (like .25") and then use your exacto to cut the line that overlaps. then remove the overlap. even if your a little bit off, by cutting, it will have a perfect butt edge. hope it helps & good luck.