Yes I think it's normal to want different people at the birth and at the appointments. I also think you need a few options because midwives have other clients and lives that can prevent them from attending the birth. Why not ask for the backup midwife to be the one you want at the birth, then ask the student to be a support person. Then your primary midwife is the one you want for antenatal.
I have known I wanted my 'team' from last time since before I fell pg and thankfully feel strongly supported. It wasn't an option to have dd's team reunite for ds due to politics in the group, so last time was new again and that was ok too.
You just need a person who you feel safe with. With my midwife I get such a sense of relief when I see her. It's like coming home.

