Голосовые и тональные вопросы

I have a few questions about the tuning and tone of the garmon.

If this information is already on a website, please give me the links and I will read.

1. Voices / Reed sets

What is the most common voice configurations?
I want to know about amateur instrument, not professional instrument with many registers.

If the right side has two voices:
Is it middle + high?

If the right has three voices:
Is it low + middle + high?
If it has a register switch, what are the two options?

What is the bass side configuration?

2. Key
The garmon can be configured in different keys.
I understand it is a transposing instrument: you press the same sequence of buttons in any key.

What is the difference in terms of practical usage?

Are certain keys preferred in certain regions or music styles?

Or does it depend on accompanying instruments and singing?

Is there a common key for the beginner?
For example, for a first garmon, is it better to be in a specific key?

Many of the teach yourself books show a picture of the buttons in "C Major". Also on this website's "Схема нот на гармони" page.
Is it better to use this tuning for a beginner?

Thank you.