1. Patch the fixtures and then set intensity/position/colour etc... Capture will remember the last state lights were in, or you can record different snapshots to recall.
2. Yes, or at least sometimes. You should be able to select the objects then replace with any library item.
3. No, capture will only open one instance. You would need two machines to work on two projects in the same version.
4. Capture does not render mirrors. You can use a reflection pane to emulate reflections but you can't do a proper mirror.
5. When you duplicate an item you can add a rotational offset. There are some guides on how to do curved video wall on the facebook group, but essentially: Select the object you want to copy; move the anchor point to the centre of the circle; duplicate with x/y/z offset as zero and a rotation that is the total angle of the wall divided by the number of panels.