a few suggestions you can do to help with your layering, after you decide on the different sizes...

-you can add, top & bottom, the closest color to the outside border to line up with the image you're placing it on for even toning (to make the photo of the screwdriver larger without making the screwdriver itself larger)

-try out the different layering options available (i.e. multiply, overlay, lighten, darken, etc.)...
can also vary these options with the use of the "opacity" level

-try your magic wand... to delete certain areas...
or your eraser in a low opacity, or even you smudge tool,
also there's "blur" which is good on softening edges

-there is also "burning" & "dodging"
(right click on each tool to see the other options you can use)

this is a good way of combining images without having to "cut stuff out", using the lasso tool, which is hard on shaky hands & the eyes

ok... well you might know some of this... a lot of is "hit & miss" & lots of practice & play to get the feel of it :] as far as your idea, it's a good premise, something there you want to say & share, so go for it!