Stereo & surround mixes in same project?

Hi everyone,
I am trying to get my first 5.1 Fiction Template done and am browsing this thread.

Fredo, what Inserts do you use on those STEM Outputs? Just Brickwall-Limiting? When using a send to route from a 5.1 Out to a Stereo out, how does it get downmixed? Or is this routing not for downmixing, just for both kinds of projects (Stereo or 5.1) and then just choose which outs to export?

How do you do up and downmixes from this? Lets say, a mix original mixed in 2.0 has to get upmixed for international use. Different session or also done in this setup?

First time professionally working in the 5.1 domain, so I am a rookie in such things.