One thing that can help your more than anything else is keep recording software running while out in the wild. Later you can review that footage and reflect on what the problem was and how to do better.

Because your balancing multiple classes, it takes much of your attention away from situational awareness. Being mobile is a huge plus. Situational but normally instant arcane explosions should do the trick for any melee on you. It's a lot to take in, while you may be fighting 2-3 people that jumped you, you weren't ready, your playing 5 guys and multiple classes at once. Your doing just fine, just takes time.

Instant cast is normally the way to go. As for fear when I did PVP I picked Horde undead for that reason. Otherwise have to grind battle grounds for the trinket. Till then if you have a dwarf in your group for fear ward, also you can dispel it with priest if it isn't feared already. Or horde again for tremor totem.