Example Entity class. The Entity class typically store all of the characteristics about your mob, like stats (health/damage), loot table, AI, and any other features you might want.
Example Render class. The rendering is fairly simple, especially if you are targeting Java 8. Any animations you might want done are handled in the model class, not the render class too.
The location of these files is completely up to you. I typically create a client rendering package holding all of my render classes and model classes, while I create a separate package for entities. Be sure to register everything properly too - you can browse some of my source code for that too.
I'm coming across one last error in the entity class. At "EntityZergling.AIHurtByAggressor" and "EntityZergling.AITargetAggressor" its says "EntityZergling. ....................... cannot be resolved to a type". Generally there would just be an import for this kind of thing, but its not picking up any classes to import. What seems to be the issue?
protected void applyEntityAI()
this.targetTasks.addTask(1, new EntityZergling.AIHurtByAggressor(this));
this.targetTasks.addTask(2, new EntityZergling.AITargetAggressor(this));