Experiences Filling Article 172 Declaration

Hello everyone! How are you?

I'm living in Sendai, Japan with a Working Holiday Visa and work freelance for a Marketing Agency in the USA (but I'm not from the USA, btw).

I have researched on the correct way to pay taxes for this work and have gone over some threads on this reddit, so I understand I need to file a Article 172 Declaration and pay around 20% of my income before March next year.

Still, I wanted to ask here if someone can share their experiences filling the Article 172 Declaration. What was the process like? Do you need an accountant? This can be hard for me since my income isn't so high.

I have experience filling my own taxes in my own country and know one thing or two, but I wanted to hear more about your guys experiences, if you have them.

Thank you!