You can't specific a node to be constrained to a rigid floor diaphragm and also provide nodal restraint at the same point in Ram Elements.
You can take that node out of the diaphragm assignment (assign it to diaphragm = 0). If that point is connected to other points by members or shells, that might be good enough.
Otherwise you can simulate the walls by actually modeling them as shells or as a stiff, short member offset from the node in question. Then you don't have to use a nodal restraint there, just restrain the far end point of this member.
When it comes to self-weight, if self-weight is assigned (to the Dead Load case typically) before generating the nodal floor mass then self-weight will influence the calculated mass, but if you turn self-weight on or change the factor after masses are generated, then it won't affect the mass.