Yes, it is necessary. If you begin the treatment at an early stage then you will not have to go for gum surgery.
Treating gingivitis will not hurt but if you have gingivitis then swollen and painful gums will be your daily pain.
Flossing, regular brushing, using mouthwash, topical cream, or gel can cure gingivitis at home.
Yes, it is curable. With daily brushing and flossing, and a meeting your dentists regularly will cure gingivitis.