Hi Michael. Yes, you'll have smooth surface results if your curves are set up properly even if you apply mirror later on. Or you could forego mirroring and draw the whole curves. The advantage of mirroring is that tweaking is less painful in that you only have to deal with half of the object especially the parts that are farther away from the mirror line. In a way I think this is another workflow alternative to have: draw your curves haphazardly then mirror or edit the curves with tools such as join, match curve or surface tangent, etc.

You mentioned joining curves. I tried it, how do you smooth out that kink where the the two curves meet?