Yeah this is a super important but sensitive topic.
I’m still doing my own research and study into these questions, so please take the following with a grain of salt or even feel free to jump in if I’ve misunderstood something.
My understanding of the historical situation is that Buddhaghosa redefined “jhana” in terms of “approach” and “absorption.”
No. Ajahn Chah is contradicting the vital importance given to absorption by the Vsm. Very different thing.
Again, this definition of jhana is the Vsm’s, not the sutta’s.
So, this is quite backwards. It will take some time to explain why.
Remember that Burma adores the commentarial tradition. So, as a Burmese meditation master, you can’t just come out and say “the Vsm is wrong” like Ajahn Chah could or even “we’ve interpreted it wrong and here’s what’s right…”
They found themselves just having to accept that “jhana” (again, contra the suttas) now simply means “absorption.” Can’t do anything about it, that’s just what it means now.
So when the Burmese say something like “you don’t need jhana” they really mean “you don’t need absorption” (same as Ajahn Chah says in the quotes above). They are not saying “samma samādhi is not the 8th step in the Noble Path.” The Burmese just typically use the Pāli terms as they’re used by Buddhaghosa.
This distinction between Vsm’s “absorption” jhanas and the EBT (“real”) Jhanas came to be known as “samatha” vs “vipassana” jhanas—I assume again borrowing language from the Vsm to “justify” this distinction and not appear to be breaking with Tradition™ even as they (in terms of practice) radically break with tradition. 
Now, that said, I myself use those terms to differentiate tranquility and insight practices as I think there is a useful distinction to be made there. This does have a canonical basis, so I personally don’t go quite as far as Keren Arbel does when she discards samatha jhanas entirely, even though I agree with her basic diagnosis.
So, actually, I personally view the Burmese vipassana techniques as likely to be very close to what the Buddha and his early disciples taught. It’s just that the terms they use to describe and justify that technique are necessarily different from the Pāli words used 2500 years ago, as those words changed their meaning during that time (as words are wont to!)
Yes, here you’re simply listing other terms the Vsm redefined. [Footnote: “Vsm redefined” is a shorthand here for a longer historical process of term drift which may have begun long before the Vsm and certainly has continued long after it.]
In general yes… but all contemporary Buddhist meditation teachers have been influenced by the Vsm Tradition in some way, so good luck escaping history!
Most people will find it very difficult to overcome their delusion without guidance from a teacher (see the aforementioned sutta) who can point out your blind spots. But, in the absence of one of those (and at the risk of getting mod-hammered for giving practical advice), by all means just read the ānāpānasati sutta and the Satipaṭṭhāna Sutta and practice what it says 
Hope that helps to clarify this somewhat.