In my case, it was really easy because we weren't that close to begin with. Over time, it just became clearer and clearer that there was absolutely nothing worth holding onto in our relationship. There wasn't even any positive nostalgia to grease the wheels -- the whole thing was a shitshow.
I'd expand on this and say that the ability to get around makes everything easier. Narcissists like to exercise control by keeping you stranded. I live in a big city now where public transit is the norm, so I have a lot of freedom now and it's wonderful.
The biggest mistake I think anyone can make with NC is trusting your heart over your mind. For instance, even though I was NC with my mother, I still spoke with my GC brother a few times out of some silly hope that he could be trusted / that I might be able to have a relationship with him. But my brain knows better -- that he cannot be trusted, and that he will lie straight to my face and feed any information I give him straight to my mother. Every time I've directly/indirectly broken NC, I've sorely regretted it for weeks. I don't make that mistake anymore.
Emotions... at first, lots of anxiety and fear. NC is a big move, and so there is naturally a fear of "oh shit how are they going to react to this?" There may be some bumps along the way, but as long as you stick to NC, all they can do is threaten, whine, guilt, etc. I recently changed my phone number, my address, my email, and locked down my social media accounts, and this helped a great deal. Over time, the fear goes away and it turns into mourning / anger/ maybe bitterness and sadness, at the waste of it all and how unfair it is. But those feelings, too, melt away as you focus more on your new life and make all sorts of improvements. Nowadays I feel totally normal and my N-family is a sort of distant memory.
Yes, I had to sacrifice other relationships, but I wasn't close with them anyway, so there wasn't much change.
My N-parents pretend like I am not NC with them. Not once has my N-mother ever asked me why I don't talk to her, etc. Even a year after NC, she would send me messages and act like we were in regular contact, as if nothing ever happened. It was bizarre. To your second question here, I just ignored them. I didn't announce anything because it would serve no use on my end. It's easier to just fall off the grid.
Not really. I just decided that I had had enough bullshit and wasn't going to play her game anymore. I didn't even care about the fear at that point -- I just wanted out. Was the best decision I ever made, though.