How to keep quality...?

[Selur]

How to setup Hybrid to keep quality using minimum possible bit-rate?[/quote9
The answer is simple, but you probably won't like it.
So not loose any quality, you need to use lossless encoding, to archive the lowest bit rate at the same time you simply need to max out all the other settings.
Problem with lossless encoding is that the output will be a lot larger than you input file (unless it also was encoded using a lossless encoding mode).

The hard truth is unless you use lossless encoding you will always lose quality.

[quote]There is something like quality/bitrate calculator in hybrid?

No, since there is no objective way to calculate 'quality' so how could there be something that measures bit-rate in relation to 'quality' ?

Since this dilemma is bugging a lot of folks, the x264 and x265 developers support something that is called 'constant rate factor' (crf) which is kind of a quality/loss indicator.
In general (assuming the other settings stay the same):

• using a lower crf means the output will loose less quality/informatio, but will be large (crf = 0 <> lossless encoding)
  
• using a higher crf value means the output will be smaller, but also loose more quality/information
  

Most folks use a crf value of 16-20 for when they encode content.

Cu Selur

Ps.: Reading http://slhck.info/video/2017/03/01/rate-control.html might help to shed some light on the bitrate distribution (rate control) modes used in x264&x265.