Okay, so I am new to this and I have a couple of questions, please bear with me & help me out?

I have written a letter that I wish to send to Ben Mansfield and I am wondering where I should send the letter to.
The fan mail address I found on here:
c/o Dalzell and Beresford Ltd, 26 Astwood Mews, London, SW7 4DE
OR, would it be possible to send it Via Venue as he is doing One Man Two Guvnors this March?
This is the address I found for the theatre:
Theatre Royal Haymarket, 18 Suffolk Street, London SW1Y 4HT
Is that where I'd send it?

I really, REALLY want him to get this letter and am also hoping for an autograph in return, so I'm wondering which address would more likely lead to a success? Or should I send it to both to be on the safe side?

Also, I want to make sure I understand this correctly:
I need to include 2 IRCs & a self addressed envelope INSIDE the envelope with his address on it, right?

And I'm also curious about the wait time for a reply. If anybody can give me a general assumption of how long I'd have to wait, that would be awesome!

I think that's all...
any help would be greatly appreciated as I intend to send this letter VERY soon. Thank you!