*Can full atheism be achieved totally or man would always look for a “god-equivalent” in his/her life?
When I see the notion of god-equivalences being raised, it is always by a theist looking an a nontheistic system. Those in a nontheistic system don’t think of things in these terms so the question doesn’t make sense unless someone outside of the system is trying to determine what the system is about. Generally, this boils down to “do atheists think things are important?” and the answer is, of course, yes. Whether or not those things are god-equivalences is harder to say.
*If most atheists are philosophers does it follow that atheism is rational?
Not necessarily, and I think you’ll need to define “philosopher” there. There are a lot of theists in philosophy departments.
*Does atheist refuse to accept God because the concept is only irrational or just because it requires quite a large moral and ethical investments?
Like anything else, it depends on the atheist but since atheists are no more criminal than any other class of people, it would seem to suggest “no” to the latter if laws are more-or-less in line with morality/ethics (a point which is always up for debate).
*If it is not logical does it follow it is not true?
No. Logic is a tool for understanding the truth but it oughtn’t be confused with the truth.
*Can atheism provide a proof that something does not exist?
It is difficult to impossible to prove that something doesn’t exist, especially if the believer is willing to go through a series of mental gyrations to keep said belief – skepticism is a bitch that way. But it is generally less about a proof of non-existence and more about alternate systems that the individual in question better models reality.
*Does atheism affirms the infinite regress?
Yes, but they don’t think that God solves it. However, since atheism is coming from a position of not-knowing, that is acceptable since they can just claim that we don’t have a good answer for that yet. Our understanding it limited, so it makes sense that there will be certain lacunae.
*Can man conceptualize something that he does not know like immortality or God?
The problem is, of course, that we do know things very much like each of these. Not having been dead, I have a pretty good idea what living is like so the continuation of that state isn’t too hard to imagine and likewise with gods we all have parents (and by-extension, authority figures we rely on) that are very much like gods in our childhood and especially in our infancy. “Our Father, thou art in Heaven . . .”