JMHO--
I simply can not fathom that this could be his first victim.
(Some graphic content here, so please skip this post if this is disturbing to you)-
The amount of detail to this crime says plainly to me that he had fantasized about doing this for a long time. IMO, this is not his first time sexually assaulting someone and encountering and manipulating a dead body. I believe that he very likely has raped other women in the past. With the amount of time he spent with her body in order to burn it, I just do not believe that he hasn't fantasized and experimented with this before. Perhaps there are some neighborhood animals missing.

I believe LE may find an extensive history on his computer of looking up violent images and websites. I do not believe a rapist who does not intend to kill the victim, can suddenly, after the death, come up with such an elaborate plan to dispose of the body. And, as others have mentioned, burning a body does take some doing- accelerant, time, etc. And most definitely, some experimentation with starting fires.
Yes, this was a crime of "opportunity", but, to me, that says that he didn't stalk Toni specifically before killing her- but likely still targeted her for some reason- some characteristic about her (a la Ted Bundy). I think he probably spent a lot of time "trolling" for an "opportunity". He didn't/couldn't lure a victim outright because he doesn't fit in with them socially, so he waited to find someone alone and vulnerable.
The fact that the neighbor says he's so nice simply indicates more strongly to me that he is a sociopath.