score:2
This reflects only my experience. I hope it helps:
Yes, if you buy in advance. Not sure how long in advance though. I bought the tickets with the standard fare. However, I did some simulations, and I was able to find cheaper tickets if booking well in advance.
Not sure, but the train I used was quite full all the way (2nd class). All seats were full in my wagon. I would say it's advisable to buy in advance. Of course, this might depend on day / hour. I travelled from Fes to Casablanca, Friday at ~11h
It's easy to buy online. Probably easier than in the station if you don't know the local practices and language.