Well, I'll try and answer your questions as best as I can.

I found that most of my assassinates I hit if I just stalked the person right. There were some people that were harder to land it on than others. Dungard was one who I never got, ditto for Igbah. I think anyone who had Maelstrom also was a really tough one to land it on. Other than that, if you stalk right, it can be very simple. I won't give away more than that, as what I've learned about stalking and such I read on forums and pieced it together.

This was my first high level assassin in a long time, since a lot of changes. I've been playing this game since Assassins had hellfire, and my first hero ever was an assassin. This was the first assassin that I really focused on assassinate. I was at 97% from 31 successes when I deleted. I wanted to hit 100 but I found it was getting tough, and my head just wasn't in it anymore. Anyway, hope that helps.