Fully commit to making a splash? (4,3,6)
I believe the answer is:
take the plunge
This could be a double definition.
'fully commit' is the first definition.
(taking the plunge means committing to something)
'making a splash?' is the second definition.
I know that 'splash' relates to this answer.
'to' is the link.
(Other definitions for take the plunge that I've seen before include "Summon up courage" , "accept the challenge" , "to leave the board" , "Get married (informal)" , "Resolve to do something irrevocable" .)