You can do either or both. I'm sorta anal about adding a single block. Sometime you really need to add two to balance it out if you have two different blocks in the quilt or if they form another pattern when put together. Borders are easy to add to it and if can use a piano key border using scraps from the quilt, it's a great way to use up scraps but some quilts don't look right with one.Remember though if you are using a pattern, don't cut out borders until you add the blocks to make the quilt larger because the borders in the pattern will be too short once you add the blocks and you will need to cut them longer.