Congratulations!

You're on the right track for accumulating points in various programs that you can in turn translated into SQ miles. I hate to say this, but it might be a bit late in the game if you're just starting to accumulate those points now, as it's best to try to redeem any airlines' miles when the window for award flights open, for most airlines about 330 days in advance. But it's still worth the effort, in that sometimes award seats are available closer in and even if SQ doesn't happen you can still try other airlines, obviously.

Having said that, the other main option is Starwood, where if you spend sufficiently on its personal and business cards (albeit perhaps a hefty $5K over three or four months???) you can convert the 25K miles for each to SQ and other airlines' miles, at the nice rate of 20K Starwood points = 25K airline miles.

Another bonus option is the Chase Ink business card.

And check out the Korean airline personal and business card bonuses, via US bank. Korean has the advantage of having comparatively good award availability, even far less than 330 days in advance. Those sign-up bonuses won't get you enough for business or first class flights, but you can top them up with, I believe Chase Ultimate Reward points (and perhaps Starwood as well?).

I guess the only thing is that all of this would be helped a lot if your fiance's credit is sufficient to at least get a few cards with bonuses. Your respective credit ratings won't take serious enough hits to hurt you unless you're planning on taking out a major loan such as for a car or house in the next year or so (in which case you might have to pay a higher rate on the loan).

Good luck!