1. I guess it depends on the situation. I assumed N3 was very easy, because I passed N1 with ease. I don't really like to bring it up, because it sounds like bragging, but that's my experience at least. Maybe using the language in a professional context on a day to day basis helps more than I appreciate. Then again, I'd expect some degree of familiarity to form naturally if you live here as a 社会人 of sorts.

2. True, but the credit is only up to a certain amount AFAIK. And still having to file taxes to the IRS every single year sounds annoying. (But I don't know. I'm not American.)

Any tips for passing the N1 with ease? It seems daunting..

Nothing special or insightful, but a few thoughts come to mind...

1) Having a limited vocabulary was one of the more long term challenges. What worked was simply developing a habit of consistently looking up any unknown words overheard or read. Whether jisho.org via Google or Google Translate or a dedicated app doesn't really matter. Either way the meaning should become clear within a few seconds. Don't wait. Just immediately look it up as soon as your hands are free. Want to speed things up? Read more. Start with manga or light novels. A bit frustrating and slow going at first, but certainly effective.

2) Train your ears with random entertainment. Configure Netflix to play Japanese content as-is without subtitles. Hear something new? Immediately pause, and apply 1) above.

3) For reading kanji the same principle applies, except looking them up can be a bit more cumbersome. There are dedicated apps (phone camera -> OCR) and tools (browser extensions) out there that automatically show furigana, which can be a life saver. (I'm hazy on the details, because I haven't had a need for them for a number of years.)

BTW, I wouldn't consider any of the above to be test preparation. Just day to day habits of living your life in a foreign country. That should get you about 80~90% there.

For the final 10~20% (test prep): 1) Use a spaced repetition program such as Anki to fill any Kanji and vocab gaps remaining. 2) Buy and read a grammar text book for some of the old-fashioned/clunky expressions that you're less likely to encounter in daily life, but nonetheless show up on N1 (and N2 to some extent).

Finally: probably best not to bother learning how to handwrite kanji. Huge effort. Not much reward or need in digital times. And of course, not part of any standardized tests either.