On the example of the cactus, I try to explain how the glow effect was achieved.
I've chosen the GI render element for that, because it already was very bright in the cactus area. As you see I started with adjusting the contrast, then I desaturated it a bit, and layered it in add mode over the original render. I put a gaussian blur onto the element, and adjusted the visibility.
The edition of the other things mentionned above were done in a similar way, some parts (eg. the red GI on the camera) had to be cut out using a mask before adjustment, in order not to affect other parts.





I hope you will enjoy this making of and find it value. Please feel free to contact me if you have any question.

Enjoy!

Anna