You Don't need any Guide in Casablanca, you will just need to book a driver through your accommodation to make sure showing you the must seen places, you would experience in Casablanca.
You might use just your guidebook and hire a Taxi driver visiting all the places you need to see and visit, it can be good to just use a Taxi agreed about a Price for 2 Hours or 3 exploring places you need to see, Most of people in Casablanca speaks French, and English.
Good Luck.

You don't need a guide or a taxi (unless you want to visit the Jewish Museum). Lonely Planet has a good walking tour.

I think the biggest issue for me is the logistics of it.

From what I can tell, the Mosque only allows visitors at specific times, the last one being 2pm. If we arrive at 12:45, I'm not sure we'd have time to get to the hotel, drop our luggage and make it to the Mosque by 2pm. Hence my thought of getting a guide to pick us up at the train station.

The earlier train leaves Fes at 6:50 am, something which I was trying to avoid. But perhaps this would just be easier.

Depends a bit on which train station and which hotel. Central Casa isn't that big, but the mosque is out towards the Corniche. If you're staying on the Corniche you shouldn't have a problem. BTW, don't take a taxi from just in front of the train station, you'll get a lousy rate.

thursdaysd- what's your best tip on getting a taxi from the Casa Voyageurs train station?
The hotel is the Le Meredian which looks to be right on the south edge of the old medina. I'm hesitant to book anything via the hotel because it's bound to be overpriced.

Kristina - pity the trains from Fez don't go to Casa Port - you could walk from the station to your hotel. But you're only 3 km from Casa Voyageurs and another 3 km from the Mosque.

From my TR (click on my name for it):

At Casa-Port train station I avoided the taxi touts who met the train, and gave up on the taxi drivers just outside, who refused to use their meters and asked double the price I expected to pay. Instead I walked a few steps to the main street and located a more amenable driver. Admittedly, I had to navigate, but the price was right.

thursdaysd-Yes, I read your trip report a while back. Didn't you have a horrible time in a riad where they would not let you leave?
I thought the same thing BTW, too bad the train does not go all the way to Casa Port or we could walk.

I don't think my mother is going to want to wander in search of a cheaper taxi.
Anyone know what we should expect to pay for a taxi from Casa Voyageurs to the Le Meredian? Are there metered taxis?