only a partial answer. I’ve been but not to watch a race. the road is wide and gentle on the valley floor until the covadonga monastery then it ramps up really steeply but its narrow like a dales or lakes climb, not a lot of space either side, not like the alps. the monastery is the last civilisation until the top. The best bit of the climb is the first 2/3s, after that it descends again into a bowl past the lakes. from the TV there never seems to be any crowds there. Then it climbs a little with an uphill sprint round a bend to a tiny wooden cafe at the top but thats it. its no alpine ski resort. cangas de onis is a pretty sizeable town for supplies.