Question: It has been my intention to define what god truly is using today's science. I need an objective opinion as to whether my argument is valid, or if you can point out where the argument is flawed.

But there is only one definition that is logically certain: "Whatever is first in existence is by definition; god".

This is not logically certain. This is just another definition of god. This would be a premise in a syllogism to define god as logically certain:

P1: Whatever is first in existence is by definition; god
P2: Something had to be first in existence
C: Therefore, god is logically certain.

P1 is just the way you choose to define god, so one can either accept or reject that. P2 is very problematic, because (currently) nobody can know if something was "first" in "existence". Therefore, we can't even get close to C.

All other definitions, abilities, attributes, or titles were given to god by Men. So we have to deem them as unreliable.

I assuming you are a man and you gave god the above definition. So...

Conversely, men also gave definitions to everything has has a definition. We would then have to conclude that everything is "unreliable," which brings us to a kind of extreme skepticism.

From our present day science, the most accepted explanation for the beginning of existence is the Big Bang. And from that event came Matter.

Admittedly, I am might not be up to date on cosmology, but as far as I recall, we know absolutely nothing about where or what the Big Bang "came from" or if it came from anything (begging the question).

... stopping there. But the common question when someone defines god that would be completely unfamiliar to any god people believe, why bother calling it "god" and confuse things?