A former agnostic, with doubts?

[Esquilax]

Argument for first cause:
Universe has a cause - we all agree on that.

Not necessarily. Again, it's entirely possible you're forcing a temporal framework upon a system that is incompatible with it. What if causation began with the big bang? What then?

Not to mention that, in cases like this where we don't have sufficient evidence to make a determination about causes and what have you, the honest answer to give is "I don't know," not "I know there was a cause."

Now what i'm transposing too, is that whatever created the universe, let's call it multiverse, either had a cause(begin), or always existed. By infinite regression, we'll either have a systematically continuously transcending infinite of causation, or an eternal "supreme" entity that created everything. Either way, one of them has to be the answer if we suppose every statement is correct.

What is the justification for asserting that the cause need be an "entity"? Couldn't an unconscious cause work just as well within the framework you've suggested?

Existance of eternity:
I'm assuming here the impossibility to there have been a moment "outside" the universe where "nothing" existed. Well, mainly because of the logical impossibility of nothing creating something. So i'm basically assuming something always existed.

Why make that assumption, instead of just admitting that you don't know?

Our own "time" was created in the big bang, but nothing contradicts that time exists outside the universe, and the fact that we know both space and time can infinitely distort, and they behave like something we call "branes"/dimensions, and also according to string theory, these dimensions and more exist outside the universe, and created our universe the same way as it "probably" created infinitelly more. We're just on our own spacetime distortion "bubble".

And again, no evidence= I don't know, regardless of the speculation.

Life:
What i'm arguing here is that basically "life" is as much of a "law"/consequence of the universe as water, i think it's illogical to actually think anything in the universe isn't a natural consequence from the start.
So i can't help but wonder how come life seems to be a systematic of the universe in itself, at least in ours, probably spread through the universe.
In conclusion, i think it's acceptable to find this brilliant organization of matter into life as suspicious as a determination to the universe.

We do know that life evolves, however. There's no need to invoke a designer to reach our current levels of complexity, when we know it developed over time from incredibly simple forms.