[The_Colonel]

I've made an opposite progression from the op. I was a strong believer of upfront design, but now value iterative approach as you do.

For the first try, hack together something working, you'll learn things along the way, validate/disprove your assumptions. Iterating on this will often bring you to a good solution. Sometimes you find out that your current approach is untenable, go back to the whiteboard and figure out something different.