I'm not sure if the wire from front LED to rear lamp is in series or parallel. I just assumed series.
Many B&M LEDclamps come with a standlight, a small capacitor to store a few minutes of power.
Dynamo lamp optics are generally bike-specific and superior to the generic beams of more powerful lamps. The effect is more useful light from a dynamo lamp.
Rubber rotors wear out, you can get replacements, though its best to stock up with a couple when you buy the dynamo.
Shimano dynamo hubs are hard to service but they are well sealed. My local LBS is very good but don't like to mess with them. Bad LBS may not know the potential damage. There are some commuter-bike specialists who can do it, generally in the big bike-friendly cities.

If your dynamo pivots on a vertical axis, the the tyre can push the rotor inwards towards the tyre or outwards away from the tyre. Mounting on the rear edge of the stay, with the tyre rotating towards the rotor is more reliable.