Clarify qabli and ba'di in mistakes during prayers. When does what come and can you use just one of them for all mistakes?

Sheikh, what is the ruling on reciting Fatiha during prayers? Do we recite it in every single rakah of every prayer? Do we recite it in Nafl? Do we recite it silently in Nafl or out loud? What if the Nafl is done at midnight, should we recite it loud or silently? Do we recite it in obligatory...

Can you give an explanation on the seven virgins when Muslims die and go to jannah?