Yeah, crunch some numbers!
Off the top of my head, when you put two cogs on an AW you want them 3 teeth apart, so something like 20 and 23 is good. That splits the hub gears nicely. If you did the same rat-io in front, so 40 and 46 for example, you would get the same effect. Do that jump again, so 40 46 52 and you would double two gears and add one more. Mostly you would just add confusion. The best chain tensioner for this purpose is a rear derailleur. But really, the best thing to do is to use two cogs on the hub. This is easy and indeed much simpler than what you propose. Either way you need a rear derailleur, so why bother with a front one?
These are good points, and thanks for the input, btw. I've been thinking about it today and reached pretty much the same conclusions myself. Very likely I'll wind up going with a 1x2 to yield six speeds (for the reasons you've already made) or even simpler still, just going with the single in back/single in front and going with the tried and true straight 3-speed. I'm sometimes really good at making a simple thing much more complicated than it absolutely needs to be!