preseason amd season 7

this is mu first time in a pre season and playing a seazon from its begining, and i have a few questions:

1. do i use the preseason to experiment with stuff in ranked?
2. how much of an impact (positive or negative) will my win/loss ratio carry over to s7?
3. what determines my placement in s7? rank at the end of s6? s6 rank + pre s7 progress? is there a total reset on mmr?

please link sourses if you can when you reply, i have some ideas about what the anwsers will b, but i am looking for the real info.

tkx!