Let me reply to the first half of your post Till, the second half is obviously the necessarily generated antiparticle
Unfortunately you read my answer as pertaining to the first and second of Pauls questions, whereas they actually pertained to questions 3 and 4 in the second paragraph.
Re the generation of particles from the vacuum: Its somewhat unclear to me the extent to which reality should be ascribed such virtual particles, since they are not operationally observable. It turns out that the equations describing their effect are such that you can always remove the vacuum fields by using shwinger's source theory and similar tricks. These tricks are less intuitive, but since they exist, and since the things they refer to are, as I mentioned, not directly observable, one has to be careful. Even the Casimir effect, one of the classic demonstrations of vacuum fluctuations in action, can be explained without recourse to the mysterious little buggers.
Be that as it may, an accelerating observer observes what the inertial observer sees as empty space as full of real particles, and these particles are entangled with others elsewhere in the universe.
Personally I find it useful to believe in little virtual particles popping in and out around me. Means I'm never lonely!
Finally: There are a few philosophers doing great physics. It is often a great place to go when looking for clarification on what we do or dont understand about a theory. I often try and grab papers by Rob Clifton or Hans Halvorsen for example, if I'm trying to get into a new subject. That said, a lot of them are doing bunk, and many of them dabble in physics with little understanding. I go to 1 or 2 philosophy conferences a year, but I pick and choose them VERY carefully...
