A few extra points. At Marseille St Charles you will need to buy your ticket. Several of the staff in the Ticket Office speak good English and I am sure they are all used to dealing with requests from people whose knowledge of their language is far from good. Although lines build up there they do move quite quickly. You cold try using a machine but many first time visitors find them off-putting. Before getting on the train use oe of the yellow "compostez" machines to date stamp your ticket. Just look out for what other passengers are doing. The trains run about once an hour.
Secondly, Ibis La Ciotat is quite a way from the station and the town centre. Therefore, unless you are being met at the station you will have to take a taxi. This might be the most expensive part of the whole transfer.
I hae used the shuttle to the rail station, and while I didn't find it a hassle there are disadvantages. Firstly, at te airport you need to get a ticket from a machine (see above). Secondly there are some potentially awkward gaps in the timetable. However, it might be worth considering for your return trip as you would be able to get a through ticket from a real person at La Ciotat station. A timetable for the service is available on the Marseille Aeroport website. The money you save wold be worth a couple of drinks.