In most years, the Aubrac has snow deep enough to obscure both the footpath and the route markings. However, after the unseasonable heat wave of summer 2018 and the record snowstorm in the eastern US November 2018, all bets are off. You might luck out with dry ground. Or be buried in a snowdrift. It's a dice-roll, so keeping a close eye on the weather forecast is vital. But that's the Aubrac. Proceeding from Cahors, with its lower elevation, seems like a much more likely place to find better weather.
Do not expect other pilgrims. You will struggle to find accommodation, and local Tourist Offices may be seasonal as well. Miam Miam Dodo lists lodgings with open seasons, and their contact information. Recommend you get busy with reservation emails to see what's available.
Spain might indeed be a better plan, in January.