1. Use 'the protagonist' to substitute 'She'
2.I know actors means males. But I think 'players' refers to those who play violins or other instruments. And "stars" must be some big ones.
3.You are right, it should be 'foreigners'. I will remember this mistake.
4.if I add a comma after 'definitely', this sentence is changed to " definitely, they...", is it correct?
5.Yes, "Core" is much better than "kernel"
6.It's a typo. I intended to use "former", but type "formal".
Your are an expert of GMAT grammar. Salute to you. "Consider as" is a common mistake in GMAT test.