Loss in Trading, Tax audit

Yes you can file, there is a provision in sec 44AD that if income is less than 6% of turnover then you have to get books audited even your turnover is less than 1cr but income should be more than 2,50,000 then only audit requires but here in your case you are suffering losses so audit is not required. go with normal return.

No, in case of f&o turnover is decided based on both purcahse and sale.
I'm case with prescribed method if your case falls under tax audit then it's mandatory.

feel free to contact harisarda01 @ gmail.com