Looking to get into 8th edition

Hello Everyone,

I have been interested in 40k for a few months now and have purchased the "start collecting" necron and chaos space marine boxes. I know that things are just starting to get going for 8th edition and wanted to know from the experts what my next steps should be.

1. Do I have enough units with each box to play a balanced game with a friend?

2. What units would you recommend for expanding each army?

3. I am planning on obtaining the new codex books and rules book but are there any other game items I need to purchase to start playing?

4. Is there any other advice I should know when getting into the hobby?

Thanks for the help everyone and I look forward to some responses.