Registering a trademark

For a swift response (from a non-US Patent Attorney) to your questions:
Intellectual Property (IP)-related matters including Trademarks can be (or get) quite complicated. Gaining the necessary experience takes a considerable amount of time, even for Patent Attorneys specialising in IP...
Generally, an applicant may represent itself in legal proceeding before the Patent and Trademark Office, subject to special requirements, e. g. a juristic entity or foreign entity must be represented by a patent practitioner.
However, be aware that:
a) The application as originally is the starting point:. Thus, initial mistakes may be difficult or even impossible to correct.
b) Your time for learning to fill in the forms may be better spend.
The USPTO says:
"Proper representation in trademark matters
Filing a trademark application with the United States Patent and Trademark Office (USPTO) starts a legal proceeding that is governed by U.S. law. While an applicant may represent itself in this legal proceeding, we [i.e. the USPTO] strongly recommend that foreign applicants, and any applicants who are unfamiliar with the trademark application process, hire an attorney with expertise in trademark matters to represent them and provide legal advice." https://www.uspto.gov/trademark/trademark-updates-and-announcements/proper-representation-trademark-matters
Consider to find a US (Patent) Attorney whom you like and trust. You're likely to come across other IP matters, sooner or later.
All the best!