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!

You can probably do it yourself, but it is probably best to hire a TM attorney - the process, like patents, can be a bit overwhelming for the novice, there are particular forms to file, specimens to fie, you have to watch for deadline dates, if the mark gets rejected, you need to formulate a proper response, there are affidavits to file post registration - it's certainly not impossible to do, but you are probably better off with a TM professional.

The USPTO's TEAS system, while antiquated and with LOTS of text on almost every screen, is not terribly complicated and a non-lawyer can definitely "figure it out" inasmuch as the non-lawyer may successfully file and pay for something. That is merely procedure, however, and the true benefit of an attorney (who might breeze through the electronic filing in just a few minutes whereas it may take the uninitiated much longer) will be realized before then: evaluating mark selection, performing trademark clearance searches, and ultimately advising on exactly what to file. Moreover, as the other attorneys have mentioned, applying for a trademark registration is a legal process with the U.S. Government complete with attestations, oaths, and declarations. Engaging an attorney to review your proposed marks, qualify their registerability, selecting appropriate classes of goods / services, and filing the application does not have to be terribly expensive: absent some exotic situation, you should be able to find an attorney who can do the foregoing for well under $1,000 / mark.

It may be not difficult to file by yourself a Trademark but I suggest you to hire a Trademark Attorney because he may assist you completely from preliminary search till grant not in one but in several Countries (through Trademark Conventions or nationally) and within certain legal due dates asking you about your actual and future steps and strategy, etc.