Pipes chased into walls

I’ve no problems doing the chasing for ch pipes, wrapping them & doing the bonding before plastering.

My comment & question is-

I usually put rads on the wall first then pipe up to them.

Are there any tricks to pipe up in walls before rads are on wall? Also, should the pipes come out of the wall at 90 degrees or should the come out & point upwards?

I’ve only got 3 downstairs to do & I want them looking good!

Cheers all

Rct