To get to Saint-Véran, you can take the train to Montdauphin-Guillestre. From there, hitchhiking works quite well.
To leave Larche, please note that there is a free shuttle bus between Larche, Saint-Paul-sur-Ubaye and Barcelonnette. From there, a coach service will take you to Gap railway station.
The various accommodation options are listed in the description for each stage.