The gnome has flash, so you can plop it down in response just as your foe cracks an Evolving Wilds (it triggers off Fetchlands too)
I was wondering if I did something wrong
I'd grab a pen and have some paper handy to write on so that if you need to make notes about things that are harder to track because they aren't as visible ("Okay, I have his Teferi's Protection exiled with my Spelljack" or "Erin's graveyard contains three cards she can cast from the graveyard"), you have easy access to doing so
If the copied creature is copying something else, then Oko becomes a copy of whatever that creature copied, with the stated exception
Sylvia Brightspear can summon her mount (and friend) Khorvath Brightflame from anywhere in your deck, and both make the other much stronger in combat
It doesnt leave your tokens out the cold either, proving that anyone can wear the helm