It's cool. People recycle mods to make their own. Everything is open source. That's how we learn to mod like this. That's what's great about Minecraft. They didn't make it incredibly difficult to go into the script and check it out -- in fact Mojang encourages it. As you grow in coding, you'll learn you may still need to rely on other mods to give you an idea of how to make your own and maybe even use them as a part of your own mod. Kinda like Not Enough Items and all of those Rei's Minimap ripoffs. In Zan's Minimap (just a better version of Rei's), when running the mod, there is still a folder named "Rei's Minimap".
You may actually want to check out other mods. They may give you an idea of extra things you can add or spells you didn't think of. Like if you add some of the animals from Fantastic Beasts And Where To Find Them, you may want to check out Mo' Creatures or something to figure out the AIs. For example, coding for a Hippogriff may be confusing, so using a Pegasus's AI and tweaking it (making it eat crows or something) may give you the desired result.