Adjustment of Status - I-485

I've been reading hundreds of experiences in this website and it is actually very helpful.

However, I can't find a similar case like ours so I could kind of interpret how things are gonna go in the interview.

I am a USC and was living out of the country for years, I met my wife there and got married in July 2015 and lived there for more than a year. We entered US in September 2016, she had a B1/B2, and then we applied for i-130 and i-485 in November, had the biometrics done in March and currently waiting for the interview.

Does anybody know if this could negatively affect the USCIS decision for our case? I mean, they could say that we should have applied for the immigrant visa from overseas?

Also, I've filed my 2015 tax return as "single" by mistake. Do you think I have to file an amendment to show that we were married in 2015? I don't want them to think that I filed an amendment to fake the marriage. We have nothing to hide about our marriage, we are living together since we were married, and I don't think there is a problem in the marriage part being genuine.

Does anybody has an experience using an interpreter in the interview? My wife speaks some English, but she could very easily get nervous and mess everything. So I want to be ready just in case the interviewer turns to be not decent (for lack of better words). Can I interpret for her? Or this could be considered as a conflict of interest?

We applied in Chicago office. I hope the officers there are good, we don't like stress! I hope it goes all good and post the good news here.

Waiting for your answers.. Thanks for helpers in advance.