I clamped a piece of wood to the desk's edge to have something to push against, as having a point of stability is nice. You can see the back of the treadmill's control panel - I took a regular treadmill, dismantled it, and mounted the panel to my adjustable desk. The treadmill is propped up on blocks to get a ~12% incline; my usual pace is around 3.1-3.4mph, depending on the season/humidity. Sweat... is significant. I usually have a towel under my wrists to uh... collect the arm-runnage >_>
I'm using ball transfer units for the trackball. They're nice, but (as with all trackballs) you should clean the BTUs if you want to keep the smooth flicking. I use a 4k tv as my monitor, so flicking from one corner of the screen to the laptop screen all the way on the other side is really nice.