To answer your questions
- Yes, kinda.
- Yes, kinda again.
- I’m not sure what you mean.
Think of animnotifies as the animation equivalent of creating custom events, except the condition which triggers the animnotify is the animation playing. When you make an animnotify, you gain access to “AnimNotify_Whatever” node in the animation BP.
If you’re watching your animation repeat in the viewer, every time the progress line goes over the anim notify, it fires an event at your AnimNotify node. So, you could set yours up to Cast To Melee Monster when activated. Here’s how mine is set up: 
Mine is meant to allow you to hit attack during the animation to queue up the next attack, so I have a CustomEvent saved in my ThirdPersonCharacter blueprint connected to a bunch of other logic. When the first attack anim is played, it triggers the “SaveAttack?” notify, which then casts to ThirdPersonCharacter, which allows me to do all the logic there instead of the anim BP.
Hopefully I didn’t ramble too much but I see too many short answers on here leaving people still lost, and I figure too much info is better than too little.