Yes, it is bigger than that with the Sideloader Modpack. My latest copy is 83GB with the Sideloader Modpack and that copy is on R4.1, much older than R8.1. I still haven't updated to a newer version than that because I have been waiting for a big thing to catch my interest, like this Steam version. Also, you can pull up the search bar in the studio and find mod items, you would not find mod items if none were included already installed. The Sideloader Modpack was just some mods removed to save some space for people who don't use the studio, they were installed before the Sideloader Modpack existed, making the size of the actual game similar to what it would be if someone were to install the Sideloader Modpack if it had existed at the time.
No, it is a major step backwards. I suggest waiting until the main Better Repack is updated with a translation rip. It will still run the Japanese version of the game, which has the most modding, but it will use the same translation as the Steam version, which is literally the only benefit the Steam version has.