I built a welding table a while back with a 3x6 piece of 5/8" plate. I ended up using a pair of trailer jacks to facilitate moving it around when necessary. I welded a t-bar on the bottom of the trailer jack with the casters welded on to the bar at the ends. (One end fixed, the other end swivel casters) Now I just crank the jacks down and move the table around when I need to. I have a pretty significant height range available, so I can crank the table up higher to clear obstructions if I need to. And since the jacks are rated for 3500 pounds each, I have a pretty wide safety margin for the table and whatever is on it. When its where I want it, I just crank up the jacks and set it on the floor. Simple, easy and sturdy.
I also welded on a pair of receiver hitch tubes on both ends for accessories. I have my vice mounted to a plate welded to a receiver hitch so if I need clear space on the table, I can remove the vice easily. I can also use the vice on either end of the table, as well as mount other accessories like a buffer/grinder or really anything that can be bolted down.