Yes it's fine to use arrays and dictionaries. If you feel comfortable using them and know well about how to use them together, it can be a very useful way to control systems like quests.
You can use one array to save all the quests info, each quest as a dictionary saved inside the array.
For example:
var quests = []
func _ready():
new_quest({"Name": "Killing 10 Slimes and save 5 Villiagers", "Type": "Main_Quest", "Accomplish_conditions": [{"Type": "Kill monsters", "monster_Type": "Slime", "amount_required": 10}, {"Save NPC", "NPC_Type": "Villager", "amount_required": 5}]})
#Here is just an example of how to use arrays and dictionaries to control a big complex quests system. Using them in similar ways can do things that are not just for quests, but also for many other things in your game, like characters, spells, etc.
function new_quest(quest):
quests.append(quest)
#.....Add more methods according to how you want to construct your program. For example: quest_accomplished(quest), are_quest_accomplish_conditions_satisfied(quest), etc. It goes on and on. It's very flexisble, and you can do lots of things.
If you prefer using scenes instead of tons of infos inside arrays and dictionaries, the idea is the same, instead of adding a dictionary into the array, using an instance of the quest scene, or a dictionary like: {"Info": quest.get("info"), "node": quest}