I just installed a new FSA K-Force Light BB30 crank on my Orbea Orca. Should the wave spring washer on the left crank arm be perfectly flat? It's still got a little "wave" (not fullu compressed) in it an I'm wondering if that's OK?

yes, it's supposed to stay wavy. That's the working spring range, which ends if/when it's flat. If they wanted it to be flat they would have saved money by providing a flat washer of the right thickness.

Think about your bike or car's suspension system. Would you want to ride in either if the spring were loaded until it were fully compressed?

Thanks. This is what I thought but wanted to confirm.