1) I recommend that you do. It's not strictly necessary, though.
2a) Unity is a complex software with a specialised interface that you need to familiarise yourself with. It took me a few days, for instance, to master the simple task of shifting my view and moving across the terrain quickly. Not because it's hard, it simply needs a little practice.
2b) If you want to build a fictional course, you can start prepping a terrain, sculpt elevations, apply textures, import objects etc.
2c) Two thirds of your course design work will be accomplished without CF and with Unity alone. You might want to absorb as much of Unity as you can so that when you get CF, you can focus on CF exclusively (which will be a lot easier to come to grips with if you are familiar with Unity). Also, you will have to invest time into Unity one way or another, now or later, so you might as well do it now.
3) Up to you, really. Follow your instincts.