My question: In going NC -- what can I expect as a response from him?

It depends on the parent. Some parents don't care all that much and won't put up much of a fight. Others will freak out and try to contact the shit out of you because they sense that they're going to lose you. Usually in those situations, they try all sorts of blatantly transparent (and highly predictable) tricks to elicit a response from you.

Other parents will issue threats or try to mess with your credit or try to get you fired at work by kicking up a fuss. Some resort to stalking or trying to get information by sending mutual friends/family ("flying monkeys") to interact with you on their behalf.

It really depends, and so the best you can do is be aware of the possibilities and plan ahead accordingly.

Although we've been fairly LC, I've never straight up ignored him yet. I assume attempted phone calls, emails, social media messages. Calling Mom, my husband, messaging my friends, etc to get info about me, or playing a pity/emergency card (I assume I'll have to coach mom a bit on NOT giving him any information about me, my job, my situation, etc) Do they tend to show up at houses/get violent/threaten things? Or is it a "I can't contact you, screw you, i'm done with you, I'm going elsewhere?"

I would say that most don't get violent, especially if they don't already have a history of it. In my experience, it was mostly just a barrage of texts and voicemails about completely unrelated subjects -- attempts to see what would stick and what would get me to respond. Sometimes they'd tell me "there's an emergency, call back ASAP" with zero details. Or they'd pull a guilt trip attempt ("so-and-so's health is on the decline, they may not make it, how can you be so heartless?"), etc.