New Player / Streamer: Looking for Tips on League & Streaming

Hey guys I'm Anne aka Winky19. I'm looking for help in terms of my gameplay and also my stream.

I've been mostly playing Ahri / Annie / Morg / Sivir either mid or bot lanes but I'm really having a hard time in terms of last hitting and trading damage with enemy champions.

Someone told me that last hitting becomes easier at level 30 since you have runes and masteries so maybe that's one reason why it's hard now? (I'm just level 12)

Also my brother help me setup a twitch stream and it looks good on his high end pc but I'm wondering how it looks for everyone else who doesn't have a super nice computer. Is there any way to test the stream?

Any tips/help is appreciated. See you guys on the rift someday!!