My husband is also from Brazil, and he had his combo interview for I-751 and N-400 a few weeks ago at the Atlanta USCIS field office. Given everything you have shared, I do not think that hiring an attorney for the interview is necessary, unless you are a worrier and having a legal representative at the interview would increase your peace of mind. The evidence of your marital relationship sounds very solid. They will likely invite both of you into the interview room for the I-751 and may ask both of you questions. My husband and I were asked a few questions about how we met and who proposed, why we sold our house in California (seemed obvious, we moved to Georgia for work), and if we had any new financial co-mingling evidence since filing the original I-751 two years before (we gave the officer IRS tax return transcripts for 2021 and 2022 and quarterly joint bank account statements for the last two years). We had two very thick file folders with much more financial evidence but were not asked to provide more. Our age gap is 27 years, so much more than your 8. The officer then asked for photos which we gave him. He flipped through the photos and then said the I-751 was approved and asked me to leave. He then conducted the naturalization interview with my husband by reviewing all of the N-400 form questions, did the English test (reading: Who can vote? writing: All citizens can vote.), and asked six of the 100 history/civics questions, all answered correctly (he had studied them every evening for three months) and the interview was over. His oath ceremony was a few weeks later and he's now waiting for his US passport to be processed and delivered. If you are well prepared you have nothing to worry about. Good luck with the interview!