I think you got some great ideas for how you'd like to play it.
I think it's more of an issue if you usually drink and then you don't. It is not odd then for friends to ask, why? out of interest, or even concern, and it's not always booze pressure.
So I like Gaylene's "not tonight" because that is my situation, I have some times I do and other nights I am not having alcohol, for one of several reasons, so it would be normal for either my hosts or dinner companions to offer wine or beer, or to say, we've already ordered glasses of wine--will you have some, or whatever, and I'll just say, oh, tonight I just feel like having ____, and that's all I say, and maybe I'm lucky, but I never get any grief. If it's my very close friends I might discuss a typical reason, usually an early morning or long day or such because we share similar situations, but I don't have to.
A lot of people I'm with are "into" various dietary kicks and reforms and they love to expound upon their journeys, and also like to learn things, so often it's genuine curiosity about "what are you eating", or someone has read about or tried or is doing for fun or health--same as exercise routines, or travel, or movies, even, so I don't get too wigged out.