Off the top of my head, I can’t think of any conservative Christian marriages of my acquaintance where the wife didn’t take the husband’s last name. Even among the nominal or seculars, I know very few couples who don’t share the husband’s last name. (Although my own family is an exception. One of my cousins married a woman who hyphenated her surname, which caused my grandmother great distress and many subtextual remarks…until one of my other cousins married a secular Hindu who didn’t change her name at all and they had the audacity to send out a Christmas card signed with both of their full names. That caused a bit of a behind-their-backs stir.)
Perhaps surprisingly, given my upbringing and general conservatism, I’m pretty agnostic on marital naming conventions. The wife’s taking her husband’s name is a Western cultural tradition, but it’s only that: a tradition. It’s not mandated by the Bible, and I can’t recall ever hearing any sermons even addressing the issue. Sharing the husband’s last name doesn’t make a couple more or less married, nor does it make their marriage better or worse off, just like wearing a wedding band in and of itself doesn’t make someone married or make a marriage better or worse.
I do think that it’s best that married couples with kids all share the last name. It’s just easier to identify the family as a unit, it cuts down on confusion with teachers and other parents, and it gives kids a tangible “belonging” as a family member. As for hyphenation, it’s just cumbersome. Think of poor little Johnny taking his SATs and only being able to bubble in “Nakopokoulous-Sm” because his hyphenated name is just too frickin’ long. Not everyone can have a hyphenated surname as snappy as the Jolie-Pitts.
Of course, it’s easiest just to follow convention. (That’s why it’s convention.) If you decide not to follow convention, you should also be willing to accept that other people won’t agree with your decision and may even get confrontational/judgmental about it. Then again, I would expect people to be understanding if your fiance’s last name is, say, Fahrts or something along that line.