
Head Start - extremely helpful one-time-purchase buff that will give you a headstart on events - your primary source of new and better crusaders. Triple Tier Trouble - unlocks tier 3 objectives, mandatory. Fast Learners - 90% faster xp gain = more damage, much quicker. Extra training - you'll need to max this out eventually, its your cheapest source of levels once you start hitting MAX level with crusaders. Deep Idol Scavenger - more idols, more buffs, more talents. But for a low cost it can be a big damage buff early on Ride the Storm and Storm's building - bigger bonuses from Storm Rider buff, but these are really only important once you have a taskmaster activating Storm Rider 24/7. Not essential, but you should be using lots of buffs early on to finish missions and unlock more Endurance Training - make your consumable buffs last longer. Prospector - more epic crafting materials are important, but not a priority. Doing it again - unlocks tier 2 objectives, which is mandatory.
Overenchanted (both of these are assuming you are doing missions and getting EPs for your units).Sharing is Caring - Lots more EP as you unlock crusaders, and therefore more damage.Efficient Crusading - more idols means more upgrades.Impatience (not that essential, but helpful early on for mission EP grinding).Super Clicks - more click damage is okay, but much better when you have taskmasters clicking for you.
Set Bonus - your dps should always have 3 full slots, so this is straight dps buff.Just a general guide assuming you only have the first 2 tiers unlocked: