FYI, 5 years is not enough time to do 50 countries. It took me 10 years of traveling 6-9 months a year to break 50, and I'd say more than half of them are places I don't think I spent enough time in.
I'd recommend taking that half of the plan out, and just shorten it to "travel for 5 years or so". Chances are you'll find at least one country that traps you for an entire year. Probably best not to set yourself up to feel bad about it.