I trim my Scheffleras all the time. My Scheffleras get too leggy otherwise. I like a more "dense" plant.
If you are going to grow them under your oaks (and that's exactly where mine spend the spring/summer months), using rebar is really a great way to stabilize the pot(s). I use a 2-4' piece of rebar, depending on the height of the pot, and hammer it through the root-ball, through the bottom of the pot, and into the soil. If you have a heavy plastic or even a ceramic pot, you can easily drill a hole approximately the size of the rebar, drive the rebar through the bottom of the pot, through the root-ball, and leave it sticking out just a bit from the bottom of the pot. Then position the pot where you want it and drive the rebar into the soil.
