Using commas and pronouns correctly in "Not only because, but also" construct

Firstly, I know that there are plenty of questions concerning "not only, but also" construct on StackExchange. However, none of them could give me an explanation for what I am trying to figure out...

How much complementary information is required when we are constructing a sentence with "not only because,.. but also"? What I mean by that is, do we need to use the same pronoun in both parts of the sentence, do we need a comma after the first principle clause?

1.) X theories are one of the most decisive for the Y industries (,) not only because they help us develop an understanding of Z, but also propose schemes for...

2.) X theories are one of the most decisive for the Y industries (,) not only because they help us develop an understanding of Z, but also (because they) propose schemes for...

3.) X theories are one of the most decisive for the Y industries (,) not only because they help us develop an understanding of Z, but also (they) propose schemes for...

4.) X theories are one of the most decisive for the Y industries because they not only help us develop an understanding of Z, but also (because they) propose schemes for...

Are all of these alternatives grammatically correct and technically identical? Or, is there any difference in the meanings from the idiomatic point of view?

The nature of word (word groups) that follows 'not only' and 'but also' should be same. In the above example, much of the confusion will disappear if 'because' is displaced.

"X theories are one of the most decisive for the Y industries because they not only help us develop an understanding of Z, but also propose schemes for... Here, "not only help.... but also propose....."