HI Scotty, First of all, Shaft, the length is the critical bit, the roller bearing shafts are superb, so shaft Diameter, probably 4mm would suit your needs.
Coupling, the center is a U/J, with inserts of the correct size, 5mm plain for the motor, 4mm threaded for the shaft.
Prop. 60mm, Raboesch from Deans, 4mm thread.
Contact Deans, they will sort all the right bits you need into a package.
Mark