Share your experiences with me - Questions about stem export / encodig formats

[drdie]

Hi

1. what is you fav format and setting for stem export for mixing in Ardour ?
2. and then what is for mastering ?
3. there is format to export above zero peaking channels without clipping ? - specially when stem export
4. format internally used in Ardour ? and if i export to this format and use it in ardour have effect in processing speed and system power using
5. what is float option in encoding section of below screenshot - Bit number ?
6. what is double option ?

(my sample rate 44.2)