(I got no clue how wire everything up with 3 engines )
@Neil
That is a really beautiful ship, and as they say almost ready to run ! Having the shafts and motors installed saves so much hassle.
With a very small rudder and three shafts you are going to need a speed controller for each shaft and a mixer to control them all from one stick.
I would recommend the ACTion Electronics P94 (twin ESC controllers + mixer) plus a single ACTion controller for the centre shaft.
see
http://www.action-electronics.co.uk/pdfs/P94.pdf for detail description and how to wire it up.
The integral mixer gradually slows the inside prop as the rudder turns, until at full helm the inside prop stops. Allows for great maneuverability.
Some nice big sealed lead acid batteries to complete the fit. You could need several just to ballast her down to the waterline.