Hi Bruno,
I see your preparations are going well!
I went to Marrakech 2 or 3 years ago.
Personally, I’d have recommended Merzouga, especially with a group of friends! (I sent you a PM about this a few months ago) : it’s a desert full of tourists, but it’s still beautiful, and there are some great stops along the way (like Ait Ben Haddou).
For Marrakech, great choice to add a riad in the Medina to be right in the heart of the action.
We really loved the Museum of Confluences—don’t miss it (same for the Medersa).
Majorelle is super photogenic, and you’ll be surrounded by influencers

but it’s still worth seeing.
For the cooking class, we really enjoyed our time with Najla (if you can’t find her online, I can give you her details). You cook at her place, first going to the local shops in the neighborhood, and the food is delicious!
We tried the "fake" desert of Agafay and took a taxi from Marrakech (I don’t remember the exact terms, but basically, some taxis do short trips within Marrakech, while others do long trips—the fares are regulated and usually displayed on the windows. For Agafay, you need a taxi authorized for long trips).
The quad biking activity is fun in beautiful landscapes (there’s also e-biking).
There are some great spots with pools and massages on-site.
In terms of landscapes, I was blown away by the High Atlas—it’s stunning.
Have a great evening,
Pascale