User blog comment:ErrorZip/Preps for hardmode?/@comment-1863391-20120110121120

I had less than that when I entered Hardmode, but got along just fine. I was in for some very rude awakening from the clown, however, so I would recommend building a lava pit (as already suggested) composes entirely of dungeon bricks. Don't worry too much about the Corruption, its spread will be inevitable after killing the WoF (killing him will spawn an enormous amount of both Corruption and Hallow in big strips across the map). If you end up needing resources like stone or sand, but they are corrupted or hallowed on your main map, it is usually best just to make a new map.

Also, just so you know, most Hardmode enemies are harder than the standard bosses. Some (the Wyvern, specifically) are even harder than the Wall of Flesh. Be prepared.