Erm.... that's all I have?!?!?!
Is this the set ?
The track gauge for Hornby is "OO" (1:76) scale
You can use either of these buffers,
You will also need these insulated joiners
You will not need to do any soldering ( although that gives a better connection) , you could get away with using some of these.
As the track will need to be divided into probably 3 electrically isolated sections, you will need 2, as I assume you already have one connecting track with your set.
Or get 2 more of these
Another important question is , How long will the overall length of track be ?
To make the shuttle unit work, each of the "separate" sections of track will need to be at least as long as the train, especially on the return run, as the engine will now be at the rear. Preferably a fair bit longer to make it look convincing and pleasing to the eye.