I managed to do a quick linear static stress analysis of your model. The results of which you can see [here] (https://www.simscale.com/projects/ahmedhussain18/stacker_mod1). I have some points for certain improvements:
One thing I noticed was that you were missing bonded contacts due to which the simulation failed. So in my case I defined all the bonded contacts and it worked fine. Another simple work around for this case will be to merge the solid in to one so one can avoid bonded contacts (this is only applicable if you want to keep the same material for whole model, which is valid for your case). For merging the solids in to one via [Onshape] (https://www.onshape.com/) and than importing directly to workspace, please see [this] (Merging solids in Onshape and meshing) forum post.
I have used Static analysis - advanced which has more boundary condition options. By using this analysis type I managed to get rid of nodal load in order to apply simple force load. For difference between these two analysis you can see a forum post [here] (FEA boundary conditions - Calculix vs CodeAster).
As far as you are not applying the load in the direction leading to motion along z-axis, you can also take half of the model which will lead to smaller mesh size and faster solution. In that case, please make sure to apply symmetric boundary condition along the cutted sides by either applying Fixed value and constraining it only along z-axis or simply applying Symmetry plane boundary condition.
I hope this will help you in your future simulations. If you have any question/s, feel free to ask. Happy Simulating!