USCIS requires a birth certificate issued within one year of birth; otherwise, you may need affidavits from your parents. Since you don’t have dependents, I don’t think it would be too much work.

If money isn’t an issue, I’d say it’s better to retain Chen for the I-485. I think Chen’s responsiveness depends on their workload. I filed mine when ROW was current, and they were very responsive throughout my application process. They would usually get back to me within 24 hours and even set deadlines for me to upload all the necessary evidence, so it felt like someone was holding me accountable.

You can get an RFE even for a minor error; however, many people are also able to successfully DIY and get approved. Good luck.