How are you intending to fix the drive units to the cabinet?

I don't see any holes near the cut outs so I assume it's going to be wood screws or similar?

I wouldn't use self tapping screws personally. If you need to take the drive units out more than a couple of times the screws are going to get less and less secure even in MDF.  Personally I would use Hex key headed bolts (M6 or so) for the bass unit. You can get nuts that have spikes on them which the bolt draws in to the MDF to have a captured nut inside the speaker. Probably best to do the holes and fit these before you put the last side on so that you know the drive unit will just screw smoothly in to place. Self tapping screws will probably be ok for the tweeter unit however.

GTM