answer 1. If you mean which character's to play with I would say there is no best character they each have there pro's and cons.
answer 2. The most OP spammer's are Kiba(pt1 and 2), Maskedman, Tenten(pt1), Kankuro(pt1) I would not say Deidara player's are spammer's just that they don't know how to properly use him.
answer 3. There is no best support setup be creative
answer 4. I play as basically everyone but I do like using Kankuro(kage summit) with Haku & Tobi, Sasori with Deidara & Sasuke(kage summit), Chiyo,Sakon/Ukon,Tobirama
answer 5. I suggjest you finish survival to get accusomed to the game then try applying what you learned there online.
I see you never heard of a tier list. Let me see you beat a skilled player using a high tier char with Zabuza
OT
1. There is no legit chars you can spam with everyone because that's all people do, spam
2. Kiba, Masked Man, Tenten, Tobi (I've seen it all), Naruto (KB), Danzo, any puppet user
3. Defense and Attack, in the second Storm Support was cheap and useful because of Sasuke spam (now changed), Pain and Sasori (now nerfed) chakra kunai techs. Defense blocks someone trying to dash into (air or ground). People even spams chakara dashing (which can stun you if caught) The attack support knocks back for a team, ultimate, regular jutsu, or a combo
4. All Narutos, All Sasukes, Mei, Minato, Pain, Itachi Both nejis Hidan
5. Everyone spams so be sure to pick Pain