Rac4.
I would like to utilize the open c file immediately, rather than try opening the a file and then controlling it.
Don't you mean Rac1? Also, the c-file is only half-open (there's a black pawn on c5), and we can't open it by force. We should get behind the d-file with Rfd1.
Oops! I meant Rac1.
Hate to get the notation wrong.

My second choice is Rfd1. I am against a4 at this point of time.