Ethnicity, frankly, should have nothing to do with it.
That’s true, but cultural differences can be very important, and I’m not talking about kibbe and hamin.
There are different expectations from marriage between different cultural groups, even among frum Yidden. I think, for example, that Litvish should tread carefully when considering marrying Chassidish. Not that it’s ch’v wrong, or shouldn’t be done, just that you need to really look into it well before going out.
You said he’s Sefardi, but that’s also very general; there are different cultures even among different groups which are referred to as Sefardim.
As a silly example, the CR seems to be on the topic of taking out the garbage. If the man grew up in a home where it was only done by women, and she grew up in a hone where it was only done by men, they’re going to have different expectations as to who will take out the garbage.
More importantly, in their homes, there may have been different ways of showing mutual respect, which can lead to serious misunderstanding.
I don’t think any of this is my own chiddush, I think this is what the gemara means when it recommends marrying someone from the same town.
I’m not referring to the OP, hopefully it’s been ascertained that this won’t be an issue in this case, however I think the point should be made.
To reiterate, I’m not saying such marriages can’t and don’t work, I just think that both parties need to understand where each other is coming from, and make sure that they’re on the same wavelength.