So, I'm a little stuck here as my knowledge of color spaces is still rather limited.
The majority of what I do is commercial work. The final delivery that I send out is 1920x1080 ProRes 422HQ.
I shoot on the Arri AMIRA at 3840x2160 proRes 4444. Right now, I'm grading and have my monitors calibrated to REC 709. My question is since I'm shooting in 4k, shouldn't I be calibrating and grading in REC 2020? To the best of my knowledge that is the desired color space for 4k material. My only worry is when this gets delivered back in HD if colors are going to look wonky. Any help would be greatly appreciated.
What display are you using for grading? What is the ultimate distribution destination for the project?
In general, if you're a beginner, my advice is to keep it simple and just use a calibrated Rec709 monitor and forget about anything more complex just yet. Amira and Alexa work just fine in Rec709 -- it's not like certain colors are going to hit a brick wall and fall down.
If your project eventually gets sold for 4K HDR distribution, then you'll need to think about how to get there... and that's a long, complex, and expensive road.
using anything else than rec709 does NOT make sense if any one of the following is true:
a) your panel/display does not support wide gamut (P3, adobe RGB color space or similar) – you would not see it and end up with shifted color values. also note: your display needs to be calibrated correctly.
b) your target platform/outlet does not support anything else than rec709
c) your target audience uses devices which do not support anything else than rec709
keep in mind that rec709 is broadcast standard and (similar to sRGB) serves as common ground across all devices. legal/data range aside, this is usually what cameras record in and digital displays show (cinema being the exception). web and computers are sRGB full range gamma 2.2 – TV and multimedia like bluray are rec709 legal range gamma 2.4 on the other hand.
so you are already in kind of a small battle over faithful monitoring, don't add the burden of managing wide gamut color spaces on top of it :)