Which alternative phrase would work best ?

Could you tell me which you would say or how you would say them please?

1 I'll arrange for a taxi to get/be here at 8pm.
2 What company did you go through/are you here with?
3 They didn't even wait for us to leave to do that/before doing that.
4 I didn't know what time was I starting/what time I start tomorrow.
5 You wouldn't happen to be John?/You don't happen to be John?
6 This medicine treats nausea related to cancer/as related to cancer.

Thank you