They are our enemy. They are Corrupted Beings. They are using innocent angel forms to delude people and keep away from spirituality. Brothers like they are very good and helpful to each other. Like you meet someone and getting closer and closer enough to call him brother.
Candle color is not important. You can use white one or not use any candle.
You have to open your Astral hearing and your third eye first to hear and see Gods.
Scrying mirror is not needed.
You may feel demons presence by yourself.
You should do your first summoning in their day and...
It's up to Satan's mind. He doesn't accepts people back who are left him. If he accepts you again his relationship with you won't be like first time dedication.