It is very well placed for us and everyone but that is not entirely a coincidence. It is going in the anti-solar direction and the launch is scheduled to avoid getting too close to the Moon. Winter is definitely good for us in the northern hemisphere since L2 is currently high in the sky.
There’s not much detail available about what will happen to the cryogenic upper stage following JWST separation which occurs at around 30 minutes after launch. JWST is directly injected into a transfer orbit to L2 so the upper stage will probably be close by but it will probably do some form of deflection burn and JWST itself will do its first course correction at L+12.5h so the two will drift apart. There is another course correction burn scheduled for L+60h. I don’t know how bright the upper stage will be but on the first few nights I would expect it would be detectable and fairly close to the spacecraft. I’ve imaged Centaur upper stages at ranges of more than 700,000 km and the Falcon 9 upper stage at 400,000km but the Ariane upper stage is smaller I think. The Centaurs also do propellant dumps which can be interesting to watch. I assume that the Ariane stage does something similar.