I’ve just come back from Nice, and getting to Monaco is a doddle. Probably easier to buy each return ticket on the day from the machines, although I think you can probably buy in advance, specifying the date of intended travel. The ticket machines are fairly easy to use if you have a bit of basic French, but there will be people who can help I’m sure. I was told by our tour rep that tickets bought from a machine do not need validating as they are too small to fit in the validating machines, and in any case, they have the date of travel on them so are effectively only valid on that day anyway…..but I would double check this……
Trains normally run roughly every 20 minutes in both directions, but they may put extra services on on race weekend. The journey takes about 20 minutes if it stops at every stop….about 15 minutes direct.
Not sure how people will be “herded” once in Monaco station, but generally, if you are heading for Rocher (GA) or grandstands that side of the course, you need to head for the back end of the train when you get off and follow the signs for the exit in that direction.
Almost all trains going west stop at Nice for your return journey. The only trains that your ticket may not be valid for are the Inter City TGV type trains, but I’m sure there will be plenty of people around to help.
Cost was 7.20 Euros return, I think, or maybe slightly more. A very cheap alternative is to take the bus which takes longer but only cost 1 Euro each way. Tickets can be bought from the driver or in advance from tabacs. Buses run from various places along Ave Felix Faure….there is no bus station as such.
Hope this helps….but just go with the crowds and you’ll be fine.