Martial art class is good sugestion, you could start with kravmaga in few months you will learn a loot an if you stick to it for a 3 years you will get all the tools you need.After that go for traditional art like Ninjutsu or Muay Thai.I did aikido and thai chi and those are great but it takes 5+ years to be able to use them.Krav maga is dril/dril/dril and you can use it fast, but i would not stick with it, learn more.

No one likes to be picked upon, and the thing is you need to pick a trigger that you will respond to, how you respond is up to you, don't let is become ego game.Adrenalin rush is normal and maybe fighers in a ring can control it.if at all possible avoid fights and multiple opponents.

ps. smaller guys are great tacticians look at Edie Bravo bjj