Phillip.
Marks model bits is a good source of prop shafts and excellent couplings.
Howes and Cornwall model boats sell all the other gear, but there are loads more.
Cant remember how big the Triune was, motor fitment will depend on how fast you want to go.
A 2.4Gig r/c set , 2 channel, are very reasonably priced .
The Component shop does batteries and things electrical, you may find an easy wiring diagram trawling through the likely posts, or alternatively Dave Milbourn will supply you with one. Action electronics did have some very good and easy to understand diagrams on the site (now the Component shop) but just having had a quick look cannot see them. DM to advise.
The current winter special has a definitive article by DM in it regarding things electrical.
Ashley