I think I can help you with #1 at least a little because I have a character who'll be fun to hate in my own comic.
A lot of it has to do with exaggeration, I think, in both design and action. Professor Umbridge is a great example of that. For starters, she's described as being very toad-like and that's a funny description. She also has a very exaggerated viewpoint of running things. She takes every fun-sucking, unreasonable rule and dials it to eleven. Every time she shows up, you know she's going to do something unreasonably awful.
I also think that it helps to have to have two conflicting personality traits, it makes the character a lot more fun. Back to the example of Umbridge once again, she does have two conflicting personality traits. On the surface, she seems like she'd be a sweet lady. She has a polite manner of speaking, she loves all things pink, she likes sugary things, and she has a bunch of cat stuff all over her walls. However, once you get to know her, you know just how nasty and controlling she is. And the thing that tops it off is that she never drops that "I'm so sweet" motif.
To sum up, what makes a "love-to-hate" character is that you have someone who does awful things but there is a thick layer of humor to them. That's what separates these kinds of characters from one-dimensional bad-guys that people get bored with. I hope that was a little helpful, anyway.