You can cut and root any size, any thickness. Not just the wee ones. Just let the cut portions dry for about a week before planting, then don't water until there's significant shrivelage on the leaves. I root my cuttings in pure growstones, but have also done it in other inorganic substrates.
From my experience jades and ports don't fuse. I've have a couple bound already for about 3 years with no fusion unlike my ficus' which will fuse np.