I've hacksawed plenty of pipes in my day, but I've never cut a steerer tube. Margin for error is pretty tiny when it's your brand-new bike. And I don't mind giving my LBS $12 for the privilege of watching them cut it, and learning for the next time.

But because it's really long, I suppose I could cut it down a single spacer the first time, just to get a feel for the measurement and result.

It's all good.