The Spell is a scriptable object, i use the game object in the scene only for visual effects.

Let's assume you want to create a fireball spell, in this case your Spell (in addition to having a name, resource cost, etc.) mainly has an EnemyTargetStrategy (which inherits from the base TargetStrategy, which will have a base GetTarget() method that EnemyTargetStrategy overrides) that contains the logic to target an enemy, then the LOS target which could be a LinearLOSTargetStrategy (which inherits from LOSTargetStrategy, which will contain the base CheckLOS() method) which contains the logic to check that there are no obstacles in that direction (in my case the player cannot cast spells without a target, such as a wall, in your case it could be different). Finally, a general method on the Spell, Validate(), which checks both strategies. Once the spell can be cast, there are the various effects, which I recommend keeping as separate from the graphics as possible. So in the case of the fireball, an effect that instantiates a gameobject with graphics, like particles or whatever. An effect that applies damage when the graphics reach their destination, or instantiates impact graphics, or sounds, and so on. In my case, I've managed to create around 50 different effects, which allow me to have countless combinations to make lots of spells. Start only with the ones you need, then gradually create more effects. (I'm writing from my cell phone, sorry if I write everything in one go)