how quickly do the capacitors charge for the standlight
The capacitors last longer than they take to charge if you're in town and only need a bright "be seen" light, this makes it a great commuter light. You'll find your light bright enough to be seen by after a few metres, after a full day discharging in the bike sheds, and bright enough to see with off road, after a full discharge after about "a car park" of length, and then it will be back up to off-road (or dark country road) level of brightness after a few metres. If you're in heavy traffic, as long as you move a little bit every few minutes, your light will stay on.
This only goes for the lights I have tried of course, which are the Exposure Revo, the K-Lite systems which are fully techhnical off road capable, and the new Dosun light, which I have replaced my previous B&M commuter light with, the Dosun would make a great town & touring only, fork crown mounted light.
The Dosun light has a "be seen" only standlight which (1) lasts for ages and (2) means the main light comes on in the first metre of riding! This might be the light you're after given the concerns you had.
Remember, all dynamo lights are not equal. They vary as much as battery lights, everything from a single AAA battery of light through to an Exposure MaXx-D is possible!