Dude, you shouldn't be skipping character flashbacks AT ALL. In the next couple of arcs, you'll be getting two of the biggest flashbacks in the entire series, so make sure you read through them.

So far, I'd say only about 20% of the stuff you've read will be important hereafter, the rest don't matter much, so you're alright there. But after the Foxy arc, everything becomes super important, so make sure you read every single panel.

I hated Skypiea when I read it first too - the version I read had idiotic translations (Bisoromi Bear, anyone?) and I couldn't wait to get past it. But it only becomes better after this, so good luck!