0. which repack? The name of the repack determines if it's eng or jap version.
1. yes but you need to know which version of the updater to get first.
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2. the game doesn't care where you install dlc from as long as they are for the correct version.
3. CMI works with latest version. That's the whole point of CMI. It's hard to jump on 3.x by accident so don't worry about it unless you already got a repack that was built on COM3D2.5. Even if you are on 3.x CMI can handle it but some plugins won't work. The purpose of COM3D2.5 is to be used with the KCES editor (a separate app) but there aren't any mods compatible with that new high poly body. So no uncensor either.