Use /lfg quick or /lfg advanced. The first one simply opens the request without further configuration. The second one will create a configuration channel that will allow several things to be configured.

They get deleted automatically after 24 hours if not otherwise configured (Premium required)

Yes, if not otherwise configured (Premium required), open requests, voice channels and configuration channels are getting deleted after 24 hours

Feel free to ask any question which comes in mind and is not listed in this FAQ or any Tutorial. Simply join the support discord

Yes, simply use /help command in your guild