I usually use photoshop for my layout designs. Make each item on a seperate layer so they can be moved around.
I start with a 24x8" document, for the first stage I use 32dpi to get my rough layout. each pixel is 1/32 of an inch then, pretty common for measurements.
FOr the T-sticks(Ive got the older model with the side lever) I:
make a layer with a square thats 2.5"x3.5"(the box uinder the panel, to make sure it fits)
make a layer on top of that with a 2"x2" circle(the dust washer)
make a layer on top of that with a 1.5"x1.5" circle(the ball top of the stick)
center everything
merge the layers together
For buttons, I use the same formula, with the size underneath the panel on one layer, and the size of the bezel on the top of the CP
For my spinner, its the oscar pro disk, so thats 3.5"x3.5" circle on the bottom, 2" circle knob on top
To lay everything out, I use the outside dimensions, to make sure theres room for everything.
I make all the "bottom" layers the same color so when I get it situated, I select that color, delete it, and then Im left with just whats covered/unseen on the CP, for over printing purposes
THen I blow it up to 300dpi, and its pretty jagged so I recreate those circles with proper dimensions and line em up with the jaggy originals.
I then take the layer with my circles, lock it, and move it to the top of my layers while I do the artwork