I've been in braces for just short of four years (I'm about to get them off). I used a Water Pic sporadically. It is good at removing food, but it be messy and inconvenient to use. I'm not entirely convinced it's a perfect substitute for floss. I would talk to your dentist about it.

I mostly used a combination of Superfloss (way better than floss threaders) and picks and dental brushes of various sizes. I used the Water Pic here and there, mostly when space between my teeth was too tight for floss. I also saw my dentist for a cleaning every four months. The only time I ran into problems is when I had a lot of extra stuff (power chains and the like) that ran right along my gumline. That didn't last long though. An electric toothbrush is also a must.

Congrats on getting braces. I understand all too well what a big step it is. It's been worth it though. Feel free to PM me if you have other questions.