What happens if I cast harvest season while I have a paradox engine on the battlefield? Will I still search for lands?
When you cast Harvest Season (or any other spell) while you control Paradox Engine, Paradox Engine will trigger and that trigger will resolve and untap all of your nonland creatures before the spell you cast resolves.
When Harvest Season starts to resolve, it counts the number of tapped creatures you control at that time. If you don’t control any tapped creatures at that time, due to Paradox Engine’s trigger for example, then X will be 0 and you won’t be able to put any basic lands onto the battlefield with Harvest Season.
(Note that you have a chance to tap your creatures between Paradox Engine’s trigger resolving and Harvest Season resolving. You have to have a way to do so, though, such as mana abilities on the creatures. You can’t just tap them because you want to tap them.)