I’m not a native English speaker, but I always thought an expression like “oh boy” was more self-reflective. Like you say it more to yourself than to whoever you’re talking to.
In which case, the other’s gender shouldn’t really matter?
In any case, I personally don’t feel insulted or misgendered if someone uses it in a conversation with me.
The Netherlands is generally quite friendly towards (English speaking) immigrants and expats. Almost everyone speaks English and no one really bats an eye at a non-Dutch resident in most of the major western cities (Amsterdam, Rotterdam, the Hague, etc.)
Housing is terrible though, prices are high and it’ll be hard to find something nice. One advantage for you (or any US resident), is that you’re exempt from the inburgering exam. Which means that you won’t have to learn the language and won’t be tested on your integration in Dutch society.
My partner is from abroad and they’ve experienced living here as quite pleasant. They weren’t exempt from the exam though (different non-EU nationality), which was a bit of a nuisance. But in general, reception was positive. They’ve been living here for over 16 years now.
But like most of Europe, we’ve got a far-right government right now, so there’s a lot of anti-immigration talk going round. Of course it’s only aimed at what they think are the “wrong” (Middle-Eastern and African) kind of people, so I doubt Americans would ever have to deal with it.