I find this to be a tough matchup. When olimar is just standing there, he has the advantage. Most olimars hide in thier shield to abuse that awesome shield grab range they have. Try ignoring the pikmin throws and aiming straight for him. Bite takes care of shield campers, and so does shield poking with the fair. You can also full jump fair into nair into jab (my favorite option, not nessesarily the best) Hopefully he will get hit by the jab. When edgegaurding your obvious priority is edgehogging , since olimar can't grab the ledge with his tether if someones on it. Be careful though because good olimars throw pikmin while recovering so you might need to time your roll/ledgegrab.
I personally just wait a bit (they like to recover low) and when the time is right hug the ledge. If you feel unsafe doing that, stay close to the ledge on the stage holding your shield up, and if he uses the ledge attack animation drop your shield and fsmash. If he ledgehops, reverse fsmash. Why? because chances are he will land on the other side of you, and if he doesn't fsmash even hits behind wario. Spam dair throughout the whole match aswell, its awesome.
And I really, really hate suggesting this, but sometimes if hes on the other side of the stage a wheelie ride on your motorcycle can throw off his camping.
Hope that helps. People should read this, Wario is pretty disadvantaged vs olimar.