How will an unavoidable overstay in the U.S. affect my future visa applications?

Usually, it does have an adverse affect. You need to explain and present proof that your overstay was not intentional.

Can I file for the labor visa if I have E2 visa in the USA

You should be able to do so. However, the immigration filing fees need to be paid by the employer.

Can I get a green card through my current employer?

Only with a waiver, and it probably unrealistic. Speak with an attorney.

Hi my name is {redacted} i put my asylum 1year aho but i didn't receive any latter for court date

If your case was accepted, you need to wait for the interview.

Pending asylum

Probably yes. However, you might still have to wait for several month.

Can I join army under mavni or any other programs ?

You need to ask the military people. the Mavni qualifications published to the public appear to suggest a NO as your answer. You need to work on...

Nope, unless you refile. You need to work with an attorney on this one.

Can I apply for advance parole during my DACA renewal process? The trip outside of the US will be during my current DACA period.

I would not risk it, since if you leave the country and unable to enter due to unforeseen delays, you may lose your chance to come back.

I am H1-B visa in USA. My visa is expiring on 5th August 2016. I wanted to know if amendment for location change can be applied

I would concur in that you need to get your extension granted first.

About marriage

If you entered the US legally, to begin with, this should not be a problem. You may want to contact an attorney to discuss the process further....