I'm with Unit One on this, including both early containment and fishing for Crates to avoid random Crimson/Corruption spawning.
In my only hardmode world so far, Thisbe, I waited until I had a Light Reaver Shark, about the best pre-hardmode digging tool you can get, before mining around the Crimson. I also walled off the Crimson side of each containment trench with wood* so thorn plants couldn't bridge the gap and spread Crimson across it. Thorns won't grow below a certain level (the Underground/Cavern boundary, I think) so the casing doesn't have to reach all the way to Hell.
After defeating WoF you'll need to tunnel around the new Crimson/Corruption and Hallow biomes, but you'll have hardmode ores and bars from all the Crates you fished up, so you can make gear to defend yourself while doing that.
Turns out I missed a few places while containing the "V", which meant going back to clean up after beating Plantera (when the spreading slows down to one third its early hardmode rate). No trouble; by then I had a Clentaminator and plenty of Green Solution. Now I've got Shroomite Digging Claws and can tunnel at warp speed.
There is one small drawback. You won't get random Pirate Invasion events if you never smash any altars, which you won't need to do if you play this way. Grind a little while in an Ocean biome to earn Pirate Maps to invoke them.
Yes, Bob is my uncle.
[edit] * You can use clay instead of wood, or any of a number of blocks that can't be corrupted.