There is a theoretical risk of overcharging your batteries, but in the real world your idea will work. I personally think it is way easier to blow up a capacitor than a battery with a bicycle dynamo. At least I have managed to make a 16V capacitor that was part of my bicycle USB charger (prototype only) bulge nicely.

To get back to your setup : I plan to make a similar thing for one of my bikes. My plan is to always run the dynamo (bottle model on this bike) when the lights are on, unless I feel/guess/fear that the batteries are overcharging.

The only question I have regarding your setup is why all those leds in parallel? You plan to use a dynamo that produces 6V RMS and your battery pack will have a similar voltage. Better then to put the series-paired leds in parallel (each time put 2 led in series and put x-number of those pairs in parallel). Else you risk to over-volt your leds. Have a look at www.pilom.com if you have not done so yet.

FYI : I'm not a electronics expert, but since I started tinkering with dynamo powered USB and led lights I have been fascinated by it.

Just saw your forum ID. Considering you call yourself "flammenwurfer", maybe you should be very careful after all ;-)