Everything listed below is heavily weighted by your choice of story teller. Cassie and Pheobe will start things off small and build it up while Randy will just throw shit at you and hope it makes some pretty fireworks.
The timing of raids is determined by your story teller as mentioned above, but the size and tactic of the raids are determined by your wealth and defense. Should a particular area of your base be heavily guarded, they will choose to sap a location to avoid that. While Tribals and Mechanoids will just do a frontal assault.
Illnesses like malaria and plague are quite dangerous if untreated but ultimately will pass over time providing you keep up treatments. Same with infections. Things like Gutworms MUST be treated with medicine or they will spend many seasons infected. My only experince with Gutworms was when my primary constructor contracted it for an entire season.
Food poisoning occurs when either a colonist consumes raw food, consumes badly cooked food (random chance when cooking, higher at lower levels) or I believe the sterility of the cooking area can affect the poisoning chance.
Nothing you can do about the traders situation, just hope.
I believe the difficulty to recruit is tied to a couple of things. The faction they came from, space refugee being the easiest and Tribal/Pirate being the hardest. And the population of your colony. The game tries to limit expansion by making it harder to get new people as you grow larger.
Colonists gain no mood buff from diversity in food but some foods grow at different speeds and yield different amounts of food. And others can be eaten raw with no mood loss. In my experience rice seems to be the most efficient crop. But I could be wrong.
As far as I can tell, no. Builders are stupid. My builders trap themselves in 1x1 holes all the time. Just be careful how you place down the plans/foundations. They will generally build from the side they approached from.
Greedy colonists are a pain in the ass. I more often than not just take the mood debuff. But a rooms stats are based on the size of the room, i think something like 6x6 will give the spacious room buff providing the bed isnt in the corner, the value is affected by the quality of the furniture/art in there. Using masterwork/legendary beds and art will massively increase the value. The cleanliness also affects the value. Make sure the room is kept clean as that is a massive draw on room stats.
The impressiveness stat I believe is an overall score for the room based on all the other stats.
Massive wall of text but I hope some of it helped.
Other people feel free to correct me on anything I may have gotten wrong