I know that it needs 7 blocks above, but I wanted to know how much it requires next to it. For example, can I put one dark oak (unobstructed) every block? Every other block? Every 5 blocks? This is for a manual tree farm. Are there any other requirements as well? I saw that the base doesn't need any space but the top does somewhere and haven't seen it since. How should I grow my dark oak?
According to the Minecraft Wiki found here:
Dark oak needs at least 7 spaces above (4×4 column) and must be planted as 4 saplings in a 2×2 square.
So, having four blocks of available space around the saplings should be sufficient.