I agree! Though, I do think he could possibly have done this before. But, I don't think he drugged her....I think they went to her house as part of the date and things went downhill there, fast. It's not hard to figure out where to find items he needed after she died - the trash bags, cooler, saw. It doesn't indicate to me that he's been there before or not. I would know where to look in anyone's house to find those types of items - and I'm assuming he was opportunistic in what he used. If he saw a duffle bag instead of a cooler, he would've used that, ykwim? I don't think he cased the joint in advance, even if he had indeed been there before.
I do think he fantasized about murdering a woman and dismembering her. He's an opportunistic predator, imo, more than a planning one. If a woman "acts weird," (and I'm assuming that means she didn't like his way of sexual advances), that's the opportunity he needed to put his fantasy into action. While he might not have had a plan for that particular night, he did have a "script" that he has thought out in his mind over the years.
Most people don't kill their dates. And of the people who kill their dates, it doesn't occur to most of them to dismember them. I would think the first thing that would come to mind would be to hide the body fast, not cut it up. He's "not normal," and he did think and want to cut it up.
JMOPINION.