Aside: are the extended sides available when playing without the AI multiplier, or do you just get the exact MOO1 experience?
You only get the duplicated races when using the AI multiplier. That was placed into the game as a quick hack to allow players to easily populate very large maps with more races.
Since this is a feature clone, not a clone, you will never get the "exact" MOO1 experience. I'm not exactly sure that is desirable. This is because known hacks & exploits in the original game have been removed, and it also means that the AI will play differently because it will not make the same mistakes as in the original game.
However, there is a very real and concerted effort to make this game as faithful to the original game as possible despite these adjustments. For example, the research interest mechanic is different because the original game's mechanic could be exploited with micro. The same feature is in Remnants but does not require micro to maximize. This required a formulaic change to the mechanic to remove the micro while retaining the feature.