400 years in close space , seems daunting

It looks like a fun exercise to come up with this but many basic assumptions look totally arbitrary. Did I get that right? The idea is to have an automated preparation mission to get the target planet livable before the generational ship gets there? The time scales here are so vast. So robots can prepare the target planet but still the ship's population is doing basic chores like agriculture? They allot more people to agriculture than we allot here on earth right now? I just scrolled through so maybe that's just to have people some purpose.