How many people will travel not by plane to both the start and from the end do you think? Train from Constanta to UK doesn't sound much fun on top of 4500km.
That's on top of nearly 2+ weeks off work plus however you get to Santiago De Compostela - if you were coming from the UK I don't think that's a direct flight, or it's the long ferry to Bilbao + some overland jazz.
How many people will travel not by plane to both the start and from the end do you think? Train from Constanta to UK doesn't sound much fun on top of 4500km.