>>360182279
It's decently hard when you're starting. You'll need to learn sculpting, proportional editing, and stuff like data transfer. There's like three methods of doing it and I didn't really have it stick until I used this one video: https://www.youtube.com/watch?v=yEAvSDrS_n0
Reminder your first stuff will always be messed up and the best part is because nobody here is interested in money, you'll get actual, honest help. 
Easy games to rip from are unironically going to be other unity games since you can use tools like Assetstudio to just crack open unity games no effort.