I've written an example of this for uSkyBlock's config.yml that I used on my local test server - It includes the basis of that I am thinking.
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slabs: #Might want to change to something else
description: Collect 64 stone slabs, 64 sandstone slabs, and 64 oak wood slabs.
rankLevel: Easy #Probably will want to change
type: onPlayer
requiredItems: 44:0:64 44:1:64 126:0:64
takeItems: true
itemReward: 43:8:24 43:9:24 43:2:24
rewardText: 24 double stone slabs with the top texture on all sides, 24 sandstone slabs with the top texture on all sides, and 24 stone wood slabs.
currencyReward: 100 #Might want to change
permissionReward: none
repeatable: true
xpReward: 100 #Might want to change
repeatItemReward: 43:8:24 43:9:24 43:2:24
repeatRewardText: 24 double stone slabs with the top texture on all sides, 24 sandstone slabs with the top texture on all sides, and 24 stone wood slabs.
repeatCurrencyReward: 10 #Might want to change
repeatXpReward: 20 #Might want to change





