Okay, a few theories that (sort of) explain away some of these technical errors (or mistakes, take your pick 😀):
1) The stranglehold that Spike had Drusilla in wasn't in order to choke her but to cause her pain, from which she passed out. Okay, why he didn't just punch her again i've no idea, given this was Spike and Dru we are talking about, but the pain theory works anyway.
2) As mentioned several times in Buffy and Angel, vampires can and do get drunk and therefore there must be some sort of blood flow going on in their bodies, just not caused by the heart. This is also apparent in the fact that vampires can have sex, for the male vampire blood flow would be kind of important there too! 😉
The fact that blood is flowing without the heart beating shouldn't be too hard to accept though. I mean they walk and talk but are technically dead, what is a little blood flowing compared to that?
3) The Turok Han drowning Spike issue. Well, i just saw that as more of a torture thing than anything else. I mean just because it wasn't gonna kill him doesn't mean that it was particular nice having his head constantly forced under water, right?
4)As for the breathing thing, well vampires can and do simulate breathing, obviously to help them pass as human, but that isn't the same thing as being able to take a deep breath or give somebody else mouth to mouth. The small amount of air needed to talk or even smoke is nothing compared to what Angel would have needed to do to force air into Buffy's lungs in Prophecy Girl. That is actually one of the issues discussed in this thread that i honestly don't see as being a mistake.