My TT stand is very similar but not as tall. I made square wooden columns because I stained the wood. I then put a threaded rod in the center of the column and poured concrete in the column. Allow the rod to protrude enough so as to mount the top & bottom. which is held by a washer & nut. In my case, I have a sandbox on top which covers the nuts at the top. And those on the bottom are recessed and don’t show. You will have to design your top & bottom so not to show the nut. My top & bottom are 1 1/2 in which made it easy. But that might not look as good for your purposes
Instead of concrete, you could just fill the legs with sand. And if you are going to paint it, you might be able to use a 3 or 4 inch PVC pipe for the legs. Or, a square vinyl tube. I’d check to make sure the PVC filled with sand does not have any ring to it before committing. Have fun