Since you said you are putting the solenoids on the side of the MWO and using a linkage, I don't think force is going to be a problem anymore. Solenoids generally have a travel of 6-10mm with max force at the final position, and the tact switches need quite a bit of force and surface area to reliably activate them BUT only need to be depressed about 2mm. That gives you an easy 4:1 or 5:1 leverage you can design in to your Frankenoven actuator linkages.
I bet a video of this thing when you get it built would go viral on Youtube... "Lazy engineer makes microwave press its own buttons"