1. Since lifting it 50 mm worked in the other simulation, it's fine.
There is a method for a boundary condition such as a Displacement to be Dead in step 1 while a force or load is applied, then for whatever unknown displacement was found at the end of step 1 to be held fixed so a different load can be applied elsewhere on the model in step 2.

2. Friction (or Rough) keeps the dead-weight from sliding around in X and Y.

3. I changed my mind after I saw that the boad was sagging below the side beams, so I unsuppressed the No Separation contacts for those, then converted them to Frictional contacts. This is runnning now and is solving very nicely.

4. Read this to understand why a large Max Ratio causes the solution to lose accuracy.

When it comes to frictional contact, Ansys seems to do better with flexible-flexible contact than it does when one side becomes rigid. My approach is to start off with rigid because it saves some computational time, but if there are convergence issues, switch to flexible.