Knowing the MF kinda goes with being a rocket scientist. I feel like those three things kinda go with the territory. Was likely picking up lots of scraps and was quite familiar with how things worked. Seems very likely that she was defending herself on a regular basis. Special? Sure. Crazy impossible unrealistically special? Not as much as you're letting on.
Spoiler for Hidden:
I can't really agree about the last part. I didn't really feel like it was out of nowhere. Here's why, there's so many indications throughout the movie that she is linked to Luke in some way. Just the fact that his light saber was pretty much calling her. Legend even suggested that she was already trained by Luke to some extent, and had her memory wiped.
No. Absolutely not. Are you telling me that of I took my car to a scrap yard they'd know how to fix a starter, transmission, ignition switch ect ect. Even if that were believable if I brought them a old junk car to repair that had a carburetor then they'd know how to fix a electric car? No no no
