Hey there!
I am rebuilding a level in Unreal 4 which I originally created in Unreal 3, but the character controller and game setup seem to be totally different. I’ve seen someone using the old character controller in a new level (movement speed, double jump, etc) as well as the rest of the game setup (weapons, pickups, bots).
How can I do this? I have been searching for this for a while but I can’t seem to find it or any information about it whatsoever. Thanks in advance 
As far as meshes and stuff like that from UDK, you aren’t allowed to use that content in UE4. As for the gameplay stuff, you have to recode it if there’s not something there in UE4, many of those things are now done with Blueprints, check out the content examples and templates.
We’re not using any meshes from UDK, we’re creating our own. People have been telling me about a plugin to use a Unreal 4 level in UDK, but they can never direct me to where to get it. 
Hmm, never heard about that plugin, but there are some programs around which will do the opposite -> UDK to UE4 
https://forums.unrealengine/showthread.php?14468-Importing-UDK-elements-into-UE4