not saying it cant be done, but i think you underestimate the time it takes to make a somewhat decent pixel art animation.
a still roughly like your example takes at the very least half an hour to make. with a minimum of 6 fps for animation you would get 36.000 individual frames for 100 minutes or 750 days of pixel art. even with a lot of duplicated assets and lower resolution this is impossible to do in 3 weeks.
4k animated pixel art
this makes me believe you dont know a lot of the medium pixel art. id suggest you look into some basic tutorials at
www.lospec.com to get an idea what pixel art is about.
and you cant simply throw assets in a animation software. stretching, rotating etc. will mess with the carefully placed pixels.
making a decent 100 min movie/animation/short film in 3 weeks is impossible in any medium. and it sounds like you expect to earn enough money from it to pay yourself and all contributers. i dont want to be mean but i honestly dont know who would be willing to pay a couple thousand dollars for something like this.