A few questions about world generating and biomes

[xxx73]

Hi guys

I have tried to find answers to the following questions but no success so far.
So here is what Im trying to find out:

1. First, I like to lower bedrock back to -57 meters as it was before, from 3 meters as it is today. How can I make bedrock deeper?
2. I really miss the old rivers and larger lakes back, but not sure possible to get back, but at least create larger body of water. What settings have to do with this?
3. Most of the water I come across in game is only a few blocks deep, I like to have deeper body of water. So how can I make water deeper?

4. Is it possible to adjust brightness for each biome individually, snow never get really dark at night.