My preferences: Dynamo hub, hardwired headlight and taillight. (best solution)

Alternate: Dynamo hub, hardwired headlight, battery taillight. (compromise, simplified wiring)

Dynamo alternate: battery headlight, battery taillight. (minimum, can usually transfer easily from bike to bike)

I don't feel a need for redundancies, but one can always add another battery light if you feel that way. Hard wired dynamo lighting, I don't feel it's necessary to have redundancy.

Legal requirements here in the US are typically Head light, tail light, rear reflector, front reflector, and spoke reflectors. Some require pedal reflectors.

I would consider a complete "system" to be lighting that meets the legal requirements in your locale.

Hub dynamo: $36 (Sanyo), Headlight: $38 (Spanninga Micro LED), Taillight: $20 (Spanninga Pixio), Wire, sundries:$10

The above will meet my minimum requirements. I have re-used spokes after cutting and re-threading them to the length required for the dynamo hub. The labor was my own. The proper comparison to this setup would be a Planet Bike Blaze front and Super Flash rear (as low as $38 for both online). The labor is a lot less on the battery lights.

My baseline for dynamo lighting is old incandescent lighting, 2.4w front, .6w rear. Anything modern and LED will beat this, easily.

Edit: I only use dynamo lighting equipped with standlight circuits.