So I have 2 questions: 1: Will the wall hold off the corruption (the wall is wood, stone brick, stone brick and wood) 2: What are the chances of corruption spawning (when I enter hardmode) on the other side of the wall?
1: Your wall will prevent the Corruption from spreading from one side to the other, yes. Wood and Gray Brick are incorruptible (even in Hardmode), and 4 blocks is the recommended wall width for preventing its spread.
2: There is, however, a chance that either Corruption or Hallow will cross your wall when Hardmode begins. The game will convert large sections of your map into Corruption and Hallow as soon as the Wall of Flesh is defeated, which may span across both sides of your wall. Additionally, each time you destroy a Demon Altar, a small pocket of Corruption or Hallow will appear in a random location on your map, and spread from there. This could happen on either side of your wall, or within the Jungle itself.
No, you are not safe. The corruption can spawn right at the edge of your jungle, crossing over the wall; after the initial burst, destroying demon altars has a chance to create corruption inside the wall, or on the other side of the jungle, near the ocean.
If, however, after breaking all demon altars you're going to, you'll find that all of the corruption is on the safe side on the wall, then yes, the jungle will be safe.