Well GunZ has been changed drastically, at least IJJI does.
Most people will startoff learning a good basic of C/C++. then you might want to do some asm but its not required.
Then you should startoff making hacks for private servers. Although i do understand if you directly go to ijji. Just search for recent leaked sources, search for tutorials how to update offsets and pointers/addresses. Then try to find help of someone like me that wants to help you. Someone that is in the recent gunz coding world. Good lick!
~ Sam