However you can expect around only 3 watts of output at normal speeds and you will need to put in around 5-7 watts of power for the same speed. This is barely enough to trickle charge modern phones.
I will probably end up with no sound system and just expensive dynamo lights, using a USB speaker that doubles up as a power brick.
There is a nice USB battery kit for dynamo that fits in the steerer, so it is soldering iron time for that, so might as well learn how to do USB-C power things.
One day there will be structural solar panel batteries that can be 3D printed into lightweight bicycle frames, so maybe I will stick to throwaway lights until then!
please don't inflict your music on everyone around you.
And there is you on your high horse telling me this?
How patronising!