That would def work, but remember a 1/2" plate of that size will not be perfectly flat and will likely warp with use. Not a problem necessarily, and tables like that are used a bunch, but something to keep in mind. If you are building one, i always like to add a section of scrap grating to them, that way you can torch out stuff right on them and the sparks blow thru, and if you are using your plasma you just ground to the table. A nice touch to add at the end of the table. I wouldn't even go a full 4x8, anything of that size you will build more accurately on jackstands, because you can level it first. You can make the jackstands by using a large threaded rod, which you can turn on your lathe. We built custom ones with 1.25" acme rod, put large castors on them so you can move them, and built a custom head for the pipe positioner, which btw is another awesome tool for fabrication, arguably more usefull than a table. Here is a vid of a guy who sells them, small handpowered ones that can easily be built using a trailer hub and ideally a cheap lathe chuck. Incredibly useful, and can be bolted to your new weld table.
https://www.youtube.com/watch?v=BB0cGCZMIfY