Those are some pretty challenging questions. #1 just requires some research into sleep tables and aggregate data, which while tedious is not necessarily difficult. #2 is worth looking into as a way to justify interest in sleep specifically.

But #3 seems impossible to answer now, since there are few enough lucid dreaming studies that likely none of them have investigated it, and I would expect any effect size to be small (which means the existing studies which use no ns <~30, for the obvious reason of it being hard to find lucid dreamers, will be badly underpowered to discover it) since lucid dreaming is fundamentally rare and dreams short in duration. It'd be like asking whether getting 30 minutes less sleep is bad for your memory: possibly, but you're going to need an awful lot of data to spot the ill effects!

Question #4 is somewhat similar but may be answerable for specific values.