Yes 1-5 is a worsetness rating, without googling it I can’t remember which end the scale starts at but the arenbergs one of the worst .
They have loads more spare wheels (plus food and bottles) than usual cos they are likely to need them. The race actually wanders all over not in a straight line so it’s a handful of guys on motorbikes or cars and as soon as the main guys go past they will leg it via a short cut to the next point further up the road.
Support cars with the directeurs still follow for most bits as well although for some bits it might be off road bikes only.
Basically it’s a silly surface to run a road bike race over but a bit like tennis on grass at Wimbledon it’s part of the appeal.