Finally finished a first full year, playing with 4-week seasons. First of all, there's an average of 1 surprise holiday per week. Spring tends to be cool for several days (except in Oasis Springs where it varies from warm to hot), and Fall tends to be warm at first. Thunderstorms seem to happen only in Summer. I did see sunsnow in Oasis Springs, but it didn't stick.
If you want to start a garden, add the gnome tradition to one of your holidays (and build a greenhouse). Mine have liked pie and coffee, and they'll drop about 20 seed packets for the rest of the day (maybe more). No rare seeds, at least not when starting out.
I still haven't done anything with bees; I'm waiting for my toddlers to become children at least.
My favorite holidays have been Lottery Day and Talk like a Pirate Day. Rebate Day is nice if your household needs some building done.
I've seen 5 different types of snowpals (10 if you count large and small versions of the same snowpal), but there could be more. Toddlers will go out and play in the snow autonomously and dress for the cold.
Your Sims will get uncomfortable inside if you don't make it warmer or cooler, but I'd wait for the moodlets to start showing up, as the thermostats do increase bills.