That's easy, place a roller-slider constraint on the bottom of each of the feet. You will have to add a small edge restraint somewhere for x-y stability of the model, say, the edge of one of the feet, and check it to make sure it isn't very much.
However, referring back to my Physics 101 days in college, this is an easy hand calculation.
It's only an easy hand calculation if you say that everything is rigid. It's not.
Your welded sheet metal is going to be so floppy that there's no way to calculate each foot loading actual loading in practice. The actual adjustment of the leveling feet will determine load on each foot. Loading will vary anywhere from teetering on 2 diagonal feet up through well-distributed on all 4 per the "easy hand calculation", depending on how level the floor is and how skilled the person adjusting the feet. If you're trying to size the feet, size them such that each foot can support the entire load by itself. That, or very close to it, will probably happen at some point in the product life.