Isn't the damage for its fall a bit high?

It should do, following the RAW falling object rules, 20d6+320d6 [340d6 or ave. of 1,190 damage]. That is 20d6 max falling plus 1d6 for every 250 pounds it weighs - 80,000 pounds divided by 250 equals 320d6 damage ...

But that's all schematics. I am jealous of your creativity.