Whats MTFB? Im guessing mean time before failure and yeah, they seem to last quite a long time.

Im not that concerned about heat. My pinball is probably the hottest place they will go and that should never go above about 30 degrees even on a hot day (yeah, our hot days are about 15 degrees!)

The on/off count i expect to be high while testing things. I always put safety switches on to cut the power to the whole playfield as soon as you lift it up and i do tend to turn things on and off a lot when im testing (maybe a few times a minute). Once everythings up and running i expect they will stay on most of the time (might turn it off at night).

How do i take care of I/Os? All my outputs will go directly into some driver chips and the inputs will go to switches with a 10K grounding resistor. Is that fine?

Whats cool startup?