The light nips are likely “love bites” since he’s not neutered. Un-neutered males will nip and circle when they are feeling frisky! He’s prob getting ready to mount you
I don’t recommend pushing his head down… That will likely disrupt the bond you are building with him and won’t work.
The nip when you reached in his cage was because he felt threatened and didn’t trust you at first. Some bunnies get very territorial over their cages, so it’s best to only do cleaning or rearranging when they aren’t in the cage.
If the light nipping bothers you, getting him neutered should help (it can also help with territorial behaviors and marking). In the meantime, to communicate that he is hurting you, you can “scream” like a bunny (look it up on youtube if you’ve never heard it, but it’s very sad
). It’s more like a loud squeak than a human scream. When a bunny gently nips another one, they have so much fur that it’s more like a nudge or a light pinch, so they don’t realize that they are hurting you. The idea with “screaming” is to help them realize they are hurting you.
My girl used to nip me on the feet when I was in her way, but once I screamed she never nipped me again! But then again I am also more aware of when I’m in her way 
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The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.