Grammar help please, dealing with brackets?

For the sake of argument say I have a sentence like the one below. How should I punctuate it?

We spoke about his job as a project manager for a building company. It sounded fascinating, (and I am not being facetious!)

It sounded fascinating, (and I am not being facetious!)

It sounded fascinating (and I am not being facetious!).

It sounded fascinating, (and I am not being facetious!).

Thanks so much

It sounded fascinating and I am not being facetious!

No brackets necessary.

I am assuming that you want to keep the brackets: there is nothing wrong with that.
Now for the punctuation. Since one cannot place a comma before a bracket, it has to come out. The second point is more complicated. Some would say that one needs a period (or full stop) after the closing bracket since the sentence ends there and the period in the exclamation point does not count as a period. I myself would consider your third alternative, given below, the correct version:
It sounded fascinating (and I am not being facetious!). But others would argue that since the exclamation point contains a period in itself, there is no need to place another period after the full stop. Had you not had the brackets, no period would have been required or used after !
Usage on this second point is not clear but I have given you my preference in the case of brackets being used.

Number Two! Everything within the parentheses its punctuated on its own and everything outside continues as if the parentheses weren't there. SO you wouldn't normally write "It sounded fascinating,." Right?

Except for the space to let Mr. Parentheses in.

Brackets, by the way, look like this:

[These are usually used to indicate a change in cited text or a parentheses within a parentheses].

It sounded facinating. (I'm not being facetious!)

The word "and" is meant to join items of equal value. The two clauses are not really equal in importance. I would leave out the exclamation point, but you may have a need for it that i don't understand.