Are there buses that I can just catch or is it better/safer to find a little tour group?
Easy. Hire a car. If that does not suit you, there are buses that regularly ply that route although for me the most comfortable, scenic and traveller friendly was taking the train. An enjoyable journey with other nationalities, including Moroccan carpet salesmen.
Easily bought return tickets while in Marrakech.
Personally I would not recommend hitching rides. If you are a westerner that can get to their country, you are already telling the locals you have money. Use it to help their economy... about 8 years ago
Yes, it is not so difficult.
By bus, there are 3 to 4 company run between Casablanca to Marrakech. CTM, Sprature, and small companies. Price is about 10euro? I don't remember but it is not so expensive. And it will take around 5-6 hours?
By train my more comfortable because you can walk around in the train. But remember, it always delay and not frequent as much as bus does.
By Grand taxi. The seats is very tight because you need to share with other 5 people (4 in back seats and 2 in front, next to driver). Cost will be around 20-30euro? It is much faster than bus. But taxi will leave only when they get the full passengers. almost 8 years ago