Hi welcome to the forum you might want to check out this thread for sco compiling [TUT] How to Compile Code + Example Scripts and theres some example scripts there and for more examples check out Three-Socks Bitbucket.
For .rpf/.img editing you will need a tool called OpenIV and ive uploaded a pack with some other tools that you might need GTAIV SCO/IMG Tools.
plus for EFLC there is 2x script.img that needs to be patched for it to work on each episode check out this thread for some more info on this [REL] Three-Socks Trainer v1.0.

