I support two CHDK scripts for focus and exposure bracketing. One for the M3 and one that should work on all other cams that run CHDK.
Deep focus bracketing with tele lenses is not recommended, ie near to hyperfocal infinity. You will end up with loads of brackets.
The beauty of the M3 is that my script runs in the background and gives you real-time info on the number of brackets you will take from the point of focus you are at. WA lenses work well.
If getting an M3, stretch and get the 11-22mm EF-M lens.