For peace of mind, I would never hire an attorney, I'd do it myself, Time after time after time we see people here in VJ asking for advice to fix their cases because the high paid lawyers they hired for "peace of mind" screwed up their cases royally. I'm not exaggerating. The lawyer isn't even the person who will fill out the paperwork, a clerk will. Having a lawyer guarantees nothing and getting "VIP" treatment doesn't mean that clerk will fill out the information correctly. I have been on this site for 11 years now, I've seen and heard it all, almost daily we have people come and say how much the regret ever hiring a so called "immigration" attorney, especially for a straightforward case. Is your brother's best friend an immigration attorney? I'm also curious why you would need a lawyer for "backup" at the interview in case there is a "misunderstanding between you and interviewer"? If you tell the truth there won't be any misunderstandings. Obviously you are free to do as you wish, but you seem so concerned about price and you think that somehow hiring a lawyer will help with your "slam dunk" case. If money is a concern and your case is so air tight, it's precisely why you don't need a lawyer.
Listen, this is a DIY site, you aren't going to find many, if any, people who tell you to hire an attorney, unless you have a complicated case. In fact, my husband and I had many so called red flags in our case and we never used an attorney during the entire journey, up to and including naturalization. I found this site after our petition had been approved and it was at the NVC, I came here to ask questions when needed, and never once did anyone steer me wrong. Not only did we DIY, we never at any point even received an RFE, I had total control over our case from start to finish. That's what I call peace of mind.