Want to marry under Special marriage Act

I am born to Hindu parents and the girl is born to Christian parents. We are agnostic by belief and do not want to follow any religion in particular (if possible, we would like to submit an affidavit in the court, stating the same). We both are living in Assam, though in two different places since over 6 months now. Her native is Assam, though mine is not. The travel distance between us is over 10-12 hours actually. Our work at present would not allow us to stay together for some time, yet we want to get wedded legally. What are our options? She would have all the documents required, but my PAN, Aadhaar etc. are not of the present address, however I have an organizational ID and even the Bank a/c Passbook of nationalized bank. Are these sufficient ? Is it necessary for parents to be a part of it from both sides? Or only any 3 witnesses are okay? As far as I know the process is to first apply in the DC office - do we have to go together for that? Can we not apply in Guwahati (neither of us are living in Guwahati though) since it would be easier for us to visit?