From Susan Tschantz
It depends on how much texture you want. You can use a thin coat of gesso to mimic plaster texture. But going too thick runs the risk of it breaking and flaking later. The more ridged the support, the less likely this is, so consider painting on a canvas covered panel. These are available through most art suppliers.
If you want a more sculptured effect, then modeling gel is better. It is designed for this, while gesso is not. You can mix acrylics into both gesso and modeling gel, but not oil paints; unless you find a modeling gel that specifically says you can mix oils with it, it’s best to assume it’s water-based.
Modeling gel remains more flexible than gesso does, so there is much less danger of cracking and flaking. Also you can embed things in the modeling gel, while you cannot with the gesso.