You'll be fine. I started out on a $700 entry level road bike, and it lasted me for a long time. In fact, I still use it as a commuting bike. Even though I do most of my riding on much nicer bikes, I still love riding my first. Riding is riding.

It seems like you like the Defy. If it's "comfortable, fast, good fit, within the budget, etc", then go for it.