Yes.

Depending on the size of the microplastic particles, they will be absorbed through the roots. Most common sources are usually contaminated water and fertilizers. Other times, regular pollution (f.e air and runoff)

Yes, and it's not just plastic either.

I shy away from buying produce from farms next to interstates.

In a grocery store, though, it's impossible to tell where something was sourced.

IIRC they're not absorbed directly, but it may influence the plant's development, etc.

Probably not that much. Though you’re probably not getting that much from eating meat as most of it should stay in the digestive tract which people usually don’t eat.

Stuff like plastic packaging, sea salt, or water is likely a more prevalent source.