How many is too many... depends where Im riding.
A cross town ride has one main front and rear (with a spare of each in case of failure) and small front and rear helmet lights.
When I used to have to go through Cannock chase at 4.30am then it was 2 mains, one for close to mid range and one for longer range, an exposure blaze on constant with a flare pulsing on the rear. Helmet light is an exposure Diablo with the rear light attachment.
You can tell me that's too much if you want, but I will put my fingers in my ears and go "LA - LA - LA CANT HEAR YOU!!!"
I should caveat that with I believe im considerate and will aim my helmet light away from oncoming traffic and also cover the long range one with my hand to avoid dazzle. the rears always stay bright as there are some boy racers and I feel safer putting a lot of light out when they approach fast on blind bends.