### Clue: Getting into part, I'm embracing challenge most profoundly — and so I should! (4,5)
### Answer: FILM ACTOR 
 ### Explanation: Definition: and so I should!
A double envelope ('getting into' and 'embracing'), of L ('chal**L**enge most profoundly'. Not my favourite construct.) in 'I'm' in FACTOR ('part'), with an extended definition.