Is killing the WOF at the edge of the world a good strategy?

No matter where you kill the Wall of Flesh the X or V of crimson/corruption/hallow that is created as a result will always be created starting from the horizontal centre of the underworld. This means that your idea of killing it at one of the edges of the world won't have any impact on where the biomes get created.

Your best bet is to create new hellevators on either side of the new biomes that are at least 4 blocks wide (I usually go for 6) to help contain the spread of those biomes. From a practical point of view you can never fully contain them because new areas of crimson/corruption/hallow can be created every time you break a demon altar.