There is also Pro Res 422 LT.
It is better to make a file up to 4 GB, then it will be successfully uploaded to all stock agencies. But, if you are interested, you can make different sizes.
Also, I am not yet sure that prores is sold better than H.264. There are also formats mov and mp4. I am also not sure that mov is sold better than mp4.
We can also talk about video resolution. Many people upload videos in 3840 by 2160. But the same shutterstock recommends uploading videos in 4096 by 2160. I don't know what sells better either.