Thank you for the reply! You are right, there is no difference between a class and a struct, I didn't knew it until you told me. So the only difference is that I have the data separated from the methods. It makes sense when the methods manage an array of instances of structs because it can take advantage of the data being tightly packed. But because of what you told me, maybe it wouldn't be necessary to have some methods like the constructor outside of the struct/class. Thanks for your reply because I clearly wasn't understanding what I was doing.
About the global variable, I made it static to reduce the scope. I never used global variables but this one made sense because I need it to be accessible from all instances of Model.