Help me to quick & deeper understand about mql5

I want to learn mql5 faster and faster, we can communicate to I have middle level understanding about mql5

language: English, chat

background me: 4 year+ experience programming, have understand about C++ and forex (mql4) (more than 1 year), now fulltime with mql5

I want to understand:

1. the behavior of experts when receive tick, what do I have when new tick is arrived, flow execute (behide the scene, not only onTick) of the mt5
2. the behavior of OrderSend in server, what happen if I call OrderSend, OrderModify?
3. common errors about when we OrderSend, OrderModify
4. what class can be used to store all information about the order we have, and how can I call this?
5. how can get best performance with OrderAsync
6. system design with expert
7. how to get better performance for EAs in mql5?