Yes for all transiting passengers depending on your flight timings

qatar is visa free now for 82 countries, check if your country comes in that list or not

(Translated by Google) A huge number of stores! (Original) Огромное количество магазинов!

Yes it is👍

Check with airlines staff , but last week I saw a guy with a guitar.

There is

Yes on arrival visa given. If you have usa or European visa you can enter doha. For sleeping you can lie down anywhere

You can go near to the food court area beside the "Coach" shop

Relaxing