My Impossible goal!

I just listened to Brooke’s homework video.
I signed up for the Life Coach School and I start in March! I’m beyond excited to get started! I have been prepping in every way that I can think of. When I was listening to her homework video I thought of my goal of making the full $18,000 back before the end of the year. Which I believe would be in what 3ish months. That goal is terrifying for me and maybe it’s too crazy out there.
I guess there’s two parts to this question.
1- How do you know if the goal you are setting is too unreachable and if it is, is that ok? I mean the idea is to fail right? But if my goal is so big I will be aiming high and pushing forward.. Which is obviously a good thing and will get me closer regardless if it takes a little longer…
2- Is it bad to set a goal that I can’t really start working towards until I’m certified? (which would be sometime in Sept I believe) Of course, doing the school work is working towards the goal but I’m worried it won’t push me to do more than I’m already planning on doing.

I am a goal-setting type of person so I could easily find another goal. But I’m so consumed (in a good way) and excited about Life Coaching that if I’m going to dedicate a ton of time and energy on anything that would be my first choice.