Is it really a bad idea for a new player to use a champion with high level difficulty? I started about 3 days ago and have since purchased Cassiopiea. I thought she'd be really fun to play and it was tough at first but now I'm getting the hang of her spells. My next purchase is going to be Zyra who is also high difficulty. I'm a little nervous since I don't want to buy a champion and then totally suck at using them. Should I just stick to easy-to-use champions for now?

It's not necessarily bad as long as you go through the process of actually learning the champ you buy. I would reccomend playing the free champs and finding who you enjoy, and then buy once you understand them a little more.

I recommend don't buy any champions until level 17-20, use free champions rotations.

I don't know why zyra is considered "difficult." I'm pretty nub, and found her easy to play, at least at lowbie levels.

For the most part, I'm sticking with free champs though I did buy a couple of cheap ones like Garen. It's the best way to see what champ or class YOU find difficult, rather than the game's description.