If you're a solo dev I think it's really important to focus on the areas where you don't have any skills. For example art, animation, effects etc. All of these could potentially be a big hurdle, depending on the idea that you are developing.
Learning how code works in Unity (as a developer) isn't that difficult, it just takes a bit of time. Say you need to add more advanced elements, for example you need some form of space partitioning? If you know the terms then searching for existing code (e.g. a good KD-tree implementation) on github is also not a problem, and you shouldn't have any issues implementing it in your game.
But figuring out what art assets you're going to need, how you're going to create them (or source them) and integrate them into the engine can be an issue. As per another comment, "juicing" the game up takes you out of your developer comfort area, you need to really tap into your creative side there.