There are a hundred and one little things that can go wrong which means you could be busy sitting on the phone etc... trying to sort stuff out, in stead of haveing your honeymoon...
My wife is a travel agent, and they see many clients like you, with a large percentage of them regretting their decision to go it alone...
I don't know about over there but here there is no margin added to the price even, the few places that still gives a margin to the agents just deduct it from the funds received...