The pickup points are mostly chosen as somewhere close to a motorway junction where it's easy to turn a coach & trailer. It might be just a lay by, so if you ride there, the coach is running late and it's raining, it might not be very pleasant. There are a couple of pickups at motorway services, which are generally accessible by bike if you can find the back entrance.
The bus itself has more leg room than standard UK coaches, but 24 hours on a coach is pretty tedious.
Panniers go in the luggage compartment under the floor, or in the bike trailer and you have no access to them on the journey. Sort what you want for the journey into a separate bag before the bus arrives at the pickup.
Valence and Orange are OK for an early (dawn) start - anywhere further north and you will probably want to book accommodation. On the return, anywhere north of Orange will be an uncomfortably late pickup.
Normal bikes are fine but there's limited space for tandems, recumbent etc that don't fit in the fitted bike racks. Water bottles & pumps can fall off en route if not strapped on, so check when you get off or take them on the bus with you.