I'm not a quantum scientist, but I don't think this is the correct view amplitude. If a configuration has amplitude -1 for electron located in some place, it doesn't mean that there's a positron there.
If your wave function at point (0,0,0) were i x delta(0) (i.e. a point-like particle perfectly located at the three-dimensional origin), the probability of finding the particle there isn't i^2, but i x i^* = i x (-i) = 1.
Doing calculations over text-based comments is so painful that I gloss over a lot, in the expectation that this isn't the right place to talk about anything but vague ideas anyway.
I hate to tell people to learn A before they can try B, but here I really, really don’t know of a way to start thinking about QFT with its positrons and annihilation and so on without getting hopelessly confused unless you’re already comfortable with normal wavefunctions-and-Schrödinger’s-equation QM. You’ll still be confused even if you are comfortable with it, mind you, it’s just that then you’ll at least have a ghost of a chance of getting your confusion down to manageable levels.
Argh. Manageable as in non-divergent, so take a small step back to regularize your confusion, and get haunted by a <https://en.wikipedia.org/wiki/Ghost_(physics)>.