Is my ESD safety procedure sufficient?
ESD is not just prevention from becoming ungrounded.  ESD events are most destructive when there is a low resistance path to follow.  The mats and straps have resistance in them to prevent a sudden discharge path when the hands touch other objects or when new components are brought into the work area.

The bare feet would be exactly wrong.  As you stand up and sit down on the stool, for example, you will now have a path for rapid discharge to the floor and secondary current flow can be rather chaotic.  Also, the bare feet make for a path for dangerous electric current in fault conditions through your body.  Really, the stool should be ESD coated and you should wear an ESD smock so that your natural movements on the stool don't become an electrostatic generator.

Keep the tabletop + computer + human as close together as possible ... electrically speaking.   The straps and mats do this.  Keep that work group as far from other unprotected objects as possible.  1 meter is a typical figure given for distance through air that friends, dogs, file cabinets and the like must be kept away.

Don't plug anything into mains any time during the assembly.  First it is dangerous due to mains coming too close to the human; and secondly, it provides a path for rapid conductivity.  The most standard approach is to connect the mat to building earth.  For this, you will have to find plumbing or other metal that gets into the ground beneath the building.  No, you can't use the ground lug of the wall outlet, that has horrible inductance to real earth and there are cases where it has been mis-wired by the original contractors.

At all times, consider your personal safety above the safety of the equipment.