Excited about a number

I am excited about a number.
I am excited about numbers in any case because I teach Maths to my year four and five children, but this is a different number.

This is my ISBN number.

I won't bore you with the number by putting it here, but let's just say it's another step towards publication. I'm not sure how many steps there have been so far, but it feels like hundreds. And getting my number was one of the micro-steps. All I had to do was apply online with the National Library of New Zealand, fill in a form, and wait.
A few days later, I received two numbers - one for the kindle edition, one for the softcover.

The next step will be my final edit when my editor has finished with the copy-editing of my novel. Hopefully that will happen in the next week.

If I had to decide on which step was the hardest in this process, I would struggle. Was is writing the first draft? Filling the gaps after the first developmental edit? Filling more gaps after the second developmental edit?
Battling the doubts in my head whether this was all worth the effort (and money)?
Launching a book cover contest and deciding on a cover?

I haven't made up my mind, and what feels quite overwhelming one day, seems completely achievable the next.

Which step has been your hardest to overcome?